If all else fails to improve a lizard's love life, try a waterbed.

That's what the folks at the San Diego Zoo did when their Komodo dragons slithered away from any romantic entanglements on the cold cement floor of their cage. The 300-pound Indonesian lizards now share a king-size (eight-foot-square) 100-degree-Fahrenheit bed. Though the lizards have yet to scale the heights of passion, "they have gotten more active," says John Andy Phillips, a research physiologist at the zoo and inventor of the beds.

The zoo's 40-odd waterbeds, now used by 100 animals including leopards, monkeys and jaguars, aren't typical. The "mattress" is coated with puncture-resistant aluminum and contains a dash of anti-freeze to prevent corrosion. The thickness of the metal depends on the strength of the occupant's jaws or claws. Hyenas, with the strongest bite, receive a quarter-inch thick mattress. Heating units are the same as those used by Homo sapiens.

Phillips installed the first bed in 1982 in the oldest sections of the zoo, where heat lamps were the sole sources of warmth. Besides using five times more electricity, the hot lamps posed a danger to the animals and disrupted their biological clocks, he says.

The zoo's rare Chinese dholes have had some of the best luck using the invention. Three pups delivered on a waterbed have survived, giving hope that these red wild dogs will escape extinction.

While the have-nots aren't exactly clawing for a bed, several animals have become quite attached to theirs. The leopards, for example, won't eat until they have dragged their ground horsemeat and occasional bone back to bed. "They've become protective; they believe the bed is their den," says Phillips. Animals at the California Primate Center at the University of California at Davis and the Toledo Zoo in Ohio will soon be testing waterbeds made by Phillips.

For animals that prefer climbing or perching, Phillips has designed an artificial tree branch that contains heated aluminum cylinders. He is also searching for a specific-wave-length light to aid mating among endangered species.

Will zoo visitors soon see mirrors on the ceilings, too? Says Phillips: "If that did the trick, we'd use them."