A pilot study using Ro 5-3350 was followed by a double-blind trial comparing Ro 5-3350 and chlordiazepoxide in a total of 25 patients who were either hospital in-patients or previous in-patients attending an out-patients follow-up clinic. The patients all had a long history of obsessive-compulsive or phobic symptoms. The visual analogue scale, the Taylor Manifest Anxiety Scale and clinical ratings were used to measure the response to treatment. In all three rating methods used, those patients who had received Ro 5-3350, chlordiazepoxide and then Ro 5-3350 in that order, consistently favoured Ro 5-3350. When the clinical ratings were examined by diagnostic groups, it was found that the phobic patients all gave favourable responses to Ro 5-3350. Two of the six patients with severe anxiety or agoraphobic states who had been treated with Ro 5-3350 over periods ranging from three to five years received the medication during the whole term of pregnancy and they were delivered of full-term normal babies. The results suggest that Ro 5-3350 (bromazepam) is a potent anxiolytic most likely to be effective in the relief of visceral manifestations of anxiety. The incidence of side-effects was low and there were no toxic effects reported.