CP-28,888-27 and placebo nasal sprays were compared in 62 normal volunteers challenged with rhinovirus type 13 or 21 in two randomized, double-blind studies. Half of the subjects received CP-28,888-27 and half received nasal placebo administered at 24, 20, and 16 h before challenge and 4 and 8 h after challenge. In each study, the number of subjects shedding virus in nasal washes, the number developing fourfold or greater serum antibody responses, and the number developing afebrile or febrile upper respiratory tract illness were not significantly different comparing subjects given CP-28,888-27 and those given placebo. Interferon was detected in nasal washes from 5 of 15 volunteers tested in the CP-28,888-27 group compared to 2 of 15 volunteers from the placebo group.