Two studies involving double-blind group comparative trials in human volunteers compared the effects of intranasal nedocromil sodium (2.6 mg active drug per nostril, q.i.d.) with placebo on clinical symptoms and performance impairment associated with the common cold. In the first study volunteers were challenged with rhinoviruses (RV9 and RV14), and in the second study with respiratory coronavirus. In both studies, active and placebo groups of volunteers were demographically similar. Infection rates in both groups were also similar. There were no withdrawals resulting from unusual symptoms related to either treatment. In the rhinovirus study (19, placebo; 20, nedocromil sodium) daily symptom scores and daily mean nasal secretion weights were significantly lower in the nedocromil sodium-treated group. In the coronavirus study (26, placebo; 27, nedocromil sodium) there was little difference in the severity of colds between the active and placebo-treated groups, but trends favoured nedocromil sodium. In both studies the impairment of performance in volunteers who developed a cold was significantly less in those treated with nedocromil sodium than in those treated with placebo.