This study was designed to test the effects of oral steroid therapy on the kinin levels and symptoms of experimental rhinoviral colds. Forty-seven men were randomized to receive prednisone (20 mg) or placebo. Therapy was administered three times a day for 5 days, after one dose was given 11 hours before inoculation with rhinovirus. Viral titers, symptom scores, and kinin and albumin concentrations in nasal washes were monitored. The mean kinin levels were lower in the steroid group (287 vs 449 pg/ml, p = 0.005) with significant differences in kinin levels on days 3 and 4 (p < 0.01). No significant difference in total symptom scores was seen between the two groups. Except for increased sneezing (p < 0.01) and mucus weights (p < 0.05) on day 1 in patients treated with prednisone, there were no significant differences in individual symptom scores. Headache tended to be less prominent in steroid recipients. Mean viral titers were higher in the steroid group (1.13 vs 0.79, p = 0.03) with significant differences in the daily viral titers on days 3 (p < 0.05) and 4 (p < 0.01). Steroids reduced kinin levels in rhinoviral infections, but that reduction was not associated with a significant reduction in symptoms. This study also provides evidence for the enhancement of viral growth in steroid recipients.