Summary 1. The compound under test, described in this paper “methadone-S,” is the sulphone analogue of dextro-methadone. 2. Animal pharmacology suggested that the drug is a fairly potent antitussive with a long duration of action. 3. Experimentally-induced cough experiments suggested that in 2 mg. doses of the drug cough suppression was no better than that produced by codeine phosphate gr. ⅙ at the end of one hour. At the end of two hours, however, the new drug did appear to be more effective. 4. A clinical trial was carried out involving 85 patients with cough. The trial terminated when the middle boundary of a sequential graph was reached indicating that there was no marked difference between the two drugs, methadone-S 2 mg. thrice daily and codeine phosphate gr. ⅙ thrice daily. 5. Subsequent analysis of the results confirmed that the new drug had no advantage over the codeine. 6. There was no marked difference in the relative incidence of side effects, except that constipation seems to occur more commonly with methadone-S and drowsiness with codeine.