Intranasal administration of enviroxime by aerosol spray was associated with drug levels in nasal secretions that 1 h later averaged 750-fold higher than those inhibitory for rhinoviruses in vitro (0.2 microgram/ml). However, administration of intranasal enviroxime (one spray per nostril, five times per day) to susceptible volunteers, beginning 1 day before and continuing for 4 days after virus exposure, did not significantly reduce infection or illness due to experimentally induced rhinovirus type 39 infection. The combined results of two separate trials yielded an infection rate of 100% for 21 placebo-treated and 89% for 19 enviroxime-treated subjects. Approximately one-half of the volunteers in each group had seroconversion to the challenge virus. Overall, 52% of the placebo-treated and 53% of the enviroxime-treated subjects developed colds. No significant differences in symptom scores, nasal mucus weights, or numbers of nasal tissues used were observed between the two groups. Two-thirds of the enviroxime-treated volunteers noted intranasal irritation immediately after sprays, as compared with only one-third of the placebo-treated subjects.