Codeine is often used as a standard antitussive against which new antitussives are compared. However there is little information available about the effects of codeine on cough associated with upper respiratory tract infection. The present study investigated the effects of codeine syrup B.P. (30 mg/10 ml, q.d.s.) or syrup vehicle on cough frequency and the subjective severity of cough during a 3-h laboratory phase and a 4-day home phase of treatment. Cough frequency and subjective scores of cough severity were significantly decreased during the 3-h laboratory phase but at no time point was there a significant difference between the codeine- and placebo-treated groups. The results of the 4-day home phase diary were similar to those of the laboratory phase as at no time point was there a significant difference between the mean scores for the codeine- and placebo-treated groups. The results indicate that codeine, either as a single 30-mg dose or in a total daily dose of 120 mg, is no more effective than the syrup vehicle in controlling cough associated with acute upper respiratory tract infection.