We conducted a multicentre, double-blind, parallel group study to compare the clinical efficacy of a new antitussive drug, moguisteine (100 mg t.i.d.), to that of a reference standard, codeine (15 and 30 mg, t.i.d.). Both drugs were given orally for a period of two days. A group of 119 patients (mean age 54 yrs; 61 females and 58 males) with chronic, dry or slightly productive cough, associated with various respiratory disorders (including chronic obstructive pulmonary disease, respiratory malignancies and pulmonary fibrosis) were enrolled at six participating centres. The percentage reduction in the number of morning coughs over a period of 6 h after the first administered dose compared to baseline assessment, was 21% with moguisteine (n = 39), 28% with codeine 15 mg (n = 38), and 29% with codeine 30 mg (n = 36). Differences between treatments were not significant. The percentage reduction in the number of nocturnal coughs per hour, after the last evening dose compared to baseline assessment, was 33, 46 and 52%, respectively. Subjective assessments (patients' visual analogue scale scores of cough frequency, cough intensity and sleep disturbance, and investigators' ranking of cough severity) indicated that there was a similar improvement in cough symptoms in all treatment groups. Adverse events were observed in two patients on moguisteine, three on codeine 15 mg, and five on codeine 30 mg. No event was serious, but discontinuation of treatment was required in two patients on codeine 30 mg. The results of our study suggest that moguisteine 100 mg t.i.d. is safe, and seems to have an antitussive activity similar to that of codeine 15-30 mg t.i.d.