Dr. Krugman's most important scientific achievements were in the unraveling of the mysteries of "infectious hepatitis." In the mid-1950's, endemic infectious diseases punctuated by epidemics were a constant cause for concern at the Willowbrook State School. The Medical Superintendent turned for assistance to Saul Krugman and his close friend and colleague, Robert Ward, as experts in infectious diseases. The problem of measles, lethal in that environment, was quickly solved with the new vaccine, which was licensed in the U.S. in 1963. Hepatitis, however, absorbed the energies of Krugman and Ward, later joined by Joan Giles, for many years.