Dextromethorphan is one of the most widely used antitussives for the treatment of cough associated with acute upper respiratory tract infection. However, there is very little data to support the efficacy of dextromethorphan in this disease state. This aim of this study was to obtain more information about the efficacy of a single dose of 30 mg dextromethorphan in the treatment of cough associated with acute upper respiratory tract infection. The study was a double-blind, stratified, randomized and parallel group design. Both objective and subjective measurements of cough were recorded over 10-min recording periods in a quiet room before (baseline) and at 90, 135 and 180 min after treatment. Forty-three patients (30 females and 13 males), mean age 22.9 years (range 18-46 years), with acute dry or slightly productive cough and otherwise healthy were included in the study. Patients were randomized to placebo treatment (n = 22) and dextromethorphan treatment (n=21). The results showed similar trends in both treatment groups with statistically significant reductions (P < 0.05) in cough sound pressure level (CSPL), cough frequency (CF) and subjective scores for cough severity within treatment groups but little difference between the treatment groups during the study period. The only statistically significant difference between treatment groups was for the mean CSPL changes from baseline to 90 min (P=0.019). There was a significant positive correlation between CSPL and CF (r = 0.752, P= 0.000) for changes in cough measurements from baseline to 90 min after treatment and this indicates that CSPL may be a useful measure of cough severity. This study provides very little if any support for clinically significant antitussive activity of a single 30 mg dose of dextromethorphan in patients with cough associated with acute upper respiratory tract infection.