Mary Shaw Shorb, 83, a biochemist, immunologist and microbiologist who was a retired University of Maryland research biochemist and the primary force behind the dramatic 1947 discovery of Vitamin B-12, died Aug. 18 at Greater Laurel-Beltsville Hospital. She had a kidney ailment.

Dr. Shorb, who had left a research career to raise a family, returned to work in 1942 during the manpower shortages of World War II. She took a post at the Agriculture Department's research station, working in its home economics and human nutrition and its dairy industry bureaus until 1946.

She lost her job, as did other female scientists, when it was reclaimed by a returning veteran.

Dr. Shorb asked the head of the University of Maryland's poultry science department for the use of research facilities to continue work she was doing on liver extracts. She had been unable to get much support or encouragement from the government.

The University of Maryland awarded her an unpaid research post to continue her work. But, as she later told a reporter, "I knew I was onto something important."

Dr. Shorb had discovered that the microbe Lactobacillus lactis thrived on tomato juice and liver extract. Her research involved the use of that concoction to locate and measure the "pernicious anemia factor."

That, in turn, was used by Merck Co. research scientists, with whom she worked, to produce commercially what became known as Vitamin B-12.

Pernicious anemia, which results in the faulty production of red blood cells, affected about 50,000 people a year in this country in the 1920s.

It was fatal until the mid-1920s, when liver extract came on the market. The extract had to be painfully and frequently injected into patients. B-12, the active agent in the extract, made treatment of the ailment less costly, less painful and much easier.

Dr. Shorb made headlines on April 16, 1948, when news of the discovery of B-12 was announced in the prestigious journal Science.

She was quickly awarded fellowships and, in 1949, a full professorship at the University of Maryland.

During her years at the university, she gained a reputation as something of a maverick. She worked long hours on research but did not teach classes. Instead, she helped guide chosen graduate students through research and academic mazes.

Her later research included work on the effects of antibiotics on poultry, the lipid content of swine parasites, food bacteriology and chick growth factors.

In 1972, she retired as emeritus research professor of poultry husbandry.

Dr. Shorb won the 1949 Mead-Johnson award, as well as awards from scientific and education groups. A resident of Beltsville, she was a member of community and parents groups in her neighborhood.

She had been active in various PTA organizations for many years and was a past president of the Prince George's Mental Health Association.

Long active in the Beltsville Women's Club, she helped organize and direct the club's drive for a new community library and had been a volunteer librarian. She also belonged to the Beltsville Garden Club.

In 1987, she was elected to the Maryland Women's Hall of Fame for her professional and community work.

Dr. Shorb was born in Wahpeton, N.D., and was a 1928 graduate of the College of Idaho in Caldwell, Idaho. She received a doctorate in immunology at Johns Hopkins University in 1933.

From 1929 to 1933, she had been a technical assistant and researcher at Johns Hopkins University, where she had worked in the School of Hygiene and Public Health.

Survivors include her husband, Doyf A. Shorb of Beltsville; a son, Alan M., of Japan; two daughters, Carole Shorb and Barbara A. Breeden, both of Beltsville; a sister, Margaret Brownfield of Boise, Idaho; seven grandchildren; and 14 great-grandchildren.