The great incidence of respiratory disease and the resultant loss of time from work or regular activities have led many investigators to seek a means to prevent this type of morbidity. We were first struck by the favorable reports of the prophylactic use of the sulfonamide drugs in both the army and the navy during the war,1even though later articles rather coolly emphasized the development of sulfonamide resistance by bacterial organisms.2 Through serving medically the members of a voluntary health insurance plan, we would have had the opportunity to try these drugs on a large civilian population and would have yielded to the temptation to do so, were it not for the reports of toxicity,1aand even of agranulocytosis and death,1bdespite the administration of small daily doses. With the advent of penicillin there came the universal recognition of its relative harmlessness, and accordingly an