Double-blind trials were conducted in volunteers to evaluate the efficacy of the prophylactic 3,4-dihydro-1-isoquinolineacetamide hydrochloride (DIQA) treatment against rhinovirus type 24 challenge. Ten men received a 7-day course of DIQA treatment and 11 men received a placebo. The intranasal viral challenge dose was 10 mean tissue culture infective doses. The oral administration of 1 g precha...