Dr. M. Lois Murphy, a pediatric oncologist whose leadership advanced early work on chemotherapy, especially for childhood cancer, and led to markedly higher survival rates, died on April 8 in New York City. She was 91.

Her death was confirmed by a spokeswoman from Memorial Sloan-Kettering Cancer Center in Manhattan, where Dr. Murphy conducted research for four decades and was chairwoman of the department of pediatrics from 1966 to 1976.

Dr. Murphy’s training in chemistry, pathology and pediatrics proved to be a good foundation for evaluating early cancer drugs. In the 1950s, working with Dr. David A. Karnofsky, Dr. Joseph H. Burchenal and other leading cancer specialists, she helped test the safety and effectiveness of 6-mercaptopurine, which turned out to be signally effective in treating leukemia. The compound led to a high percentage of remissions and remains in use.

She later helped test other cancer-inhibiting agents, including actinomycin-D, an antibiotic that was shown to interfere with the proliferation of cancer cells. That drug also remains in wide use.

Dr. Murphy subsequently became interested in the combinations of drugs as an even more promising means of treating solid tumors and leukemia, an approach that she and others in the field refined in the 1960s.

At Sloan-Kettering, Dr. Murphy also shaped the delivery of care, and argued that outpatient treatment would be more cost-effective and less stressful for children and their families. In 1968, she helped found Sloan-Kettering’s Pediatric Day Hospital, which allowed patients to spend most of their time at home. From 1969 to 1974, patient visits rose to 12,000 from 6,000 annually, and the clinic became “a first step toward the modern approach to pediatric oncology” and continues to be a model, said Dr. Richard J. O’Reilly, an oncologist and the chairman of the institution’s department of pediatrics.

Mary Lois Murphy was born on a ranch near Curly, Neb. She received her medical degree from the University of Nebraska in 1944, and was one of two women in a graduating class of 100.

After teaching at Georgetown and the University of Pennsylvania, she joined Sloan-Kettering in 1951. Dr. Murphy also held appointments at Cornell, and was named an assistant professor of medicine there in 1954. She became a professor of pediatrics at Cornell in 1970, a post she held until retiring from both institutions in 1992. She remained active and attended regular ward-teaching tours at Sloan-Kettering until last year.

Dr. Murphy lived in Manhattan and never married.

In testing cancer drugs, she observed that variations in the dosages of some compounds resulted in birth defects in laboratory rats and other animals. Dr. Murphy became an authority in the field, known as teratology, and tested thalidomide and other agents to determine how promising drugs that were intended to attack cancers could breach the placenta and potentially damage a fetus.