In a double-blind controlled trial, lidoflazine (in a daily oral dose of 240 mg for three periods of 8 weeks each) was compared to an inert preparation. 20 of 27 patients completed the double blind study. 4 patients were withdrawn from the study for unrelieved angina. Three of these patients were on the placebo and failed to respond to treatment with the active drug. As assessed by the frequency of anginal pains, nitroglycerine consumption, the anginal threshold and the extent of exercise-induced ST segment depression, lidoflazine was not found superior to the placebo. The heart rates on exercise were, however, lower after lidoflazine administration. The significance of this observation remains unexplained.