The first symptom is usually a peculiar hardening and heaviness in the victim's feet and ankles, as if they were tightly encased in some thick rubber substance. The toes seem stuck together and immovable, the feet feel as though they were strapped into very tight shoes.

Later, there are grotesque deformities of hands and legs, accompanied by severe pains. It becomes impossible to walk. speech becomes difficult and eyesight begins to weaken, ending in blindness for many.

They are the crippling results of Japan's most dreaded disease, smon, a nervous disorder that affected thousands here until a household drug believed to be the cause was taken off the market. It is by far, Japan's worst drug-caused tragedy and by some estimates may be the world's biggest drug-induced crippler.

More than 11,000 Japanese have been damaged by it in the past two decades, and yeats of litigation against drug companies and the government in 25 courts have produced record-breaking damages exceeding$100 million.

It has also evoked criticism of the government's drug-evaluating system, of the prescription habits of Japanese doctors, and of the companies that sold the damaging drug as a harmless household remedy for diarrhea.

Smon (subacute myelo-optico-neuro-pathy) outbreaks in several communities occurred as early as the 1950s. Since then, hundreds of victims have been hospitalized or confined to whellchairs and thousands more crippled so badly they cannot work. One out of 20 has gone totally blind.

The cause has been identified by medical researchers as Clioquinol, a substance used in antidiarrhea medicines all over the world for decades and said to be still widely prescribed in developing countries where drug regulations are weak.

A growing number of Japanese judges have accepted the investigators' findings and labeled Clioquinol as the cause of smon. Two drug companies and the Japanese government have in effect accepted vthat finding and offered to settle out of court, while a third drug company that marketed Clioquinol insists smon is caused by a virus.

But a major remaining question baffles the experts: Why Japan? Clioquinol has been marketed in several forms throughout the world since 1899. Small numbers of smon cases have been verified in France, West Germany, the Netherlands and Sweden. But no other country has yet reported smon on so large a scale as in Japan.

Some authorities have speculated about racial factors peculiar to the Japanese. For a time, drug companies contended that since smon did not spread in other countries Clioquinol could not be blamed. But courts are now pinning the blame on the heavy dosages prescribed by Japanese doctors.

According to the opinion of the Tockyo district court. "The large-scale outbreaks of smon in Japan can be concluded to be due to the wide use of larger daily doses and longer periods of administration in Japan than in foreign countries."

"In Japan, doctors used it as an antidiarrhea medicine and prescribed large doses of it for long periods of time," said one attorney who has represented victims. "But in other countries it was not prescribed by doctors. It was only sold in shops and kept around the house and lots of it was thrown out periodically."

(Under an informal rule which they adopted, all lawyers associated with the smon cases refuse to be quoted by name.)

In Japan, physicians are permitted to sell drugs directly to patients on their own prescription. The more drugs they prescribe, the more money they make.

A government-financed research group vpinpointed Clioquinol as the cause of smon in 1970, after finding that many patients with similar nervous disorders had taken large doses for long periods. The Japanese government promptly ordered the drug taken off the maket.

"That was a good decision," the attorney said, "But still the government is responsible because it authorized the importing and manufacturing of Clioquinol, even though it was known to have caused side effects in other countries." The government has accepted a "social responsiblity" for the injuries but contends it did not know of bad side effects when it authorized sale of medicines containing Clioquinol.

Adverse effects of Clioquinol on nervous systems were noted as early as 1935 in Argentina but it was widely used here until 1970 and was in the medical kits of Japanese soldiers in World War II. The U.S. Food and Drug Administration limited its use as early as 1961 because of suspected harmful effects, but Japan's government did not act for another nine years.

"There were cases reported [in Japan] as early as 1958, but we did not at that time after to it as smon," recalls Dr. Itsuzo Shigematsu, a prominent physician who headed the government investigation in the late 1960s. "We began calling it smon in 1964, but it was not associated then with Cliquinol." In fact, one famous Japanese doctor said the drug was a good cure for smon and prescribed it for smon patients, Shigematsu added.

Because the drug damages one's nervous system, the disease is rarely curable. Shigematsu estimates that only 20 percent of the victims -- those who has taken it for a short time -- can be cured.

Since the drug was banned in 1970, the number of diagnosed smon cases has decreased dramatically. Eight months after the prohibition order, groups of smon victims banded together and began filing suits, accusing the drug companies and the government of negligence.

More than 4,700 victims have filed 25 suits so far and they have won 20. The total damages awarded exceeds $107 million. The average award has been about 23 million yen, or $110,000 at current exchange rates -- a very large sum by Japanese standards.

Japan's government officially recognizes 11,007 victims of smon while attorneys claim there may be as many as 20,000 in the courty. Shigematsu said it may be the world's largest crippler by drugs. But experts say it may exist on a wide scale in many developing countries which do not regulate drugs diligently and which do not have many neurologists capable of performing the systematic research that pinpointed smon in Japan.