1 Methods for the investigation of possible interactions with tricyclic antidepressant drugs are described. These methods have been applied to a new compound, Ciba 34276-Ba, which has been shown to have antidepressant activity. 2 In five normal volunteers tested before and during treatment with Ciba 34276-Ba, no abnormalities of resting or post-exercise electrocardiographs occurred. A three-fold reduction in tyramine-responsiveness was seen in three normal subjects studied, but no potentiation of the noradrenaline pressor effect occurred. One of six patients given Ciba 34276-Ba whilst on long-term treatment with bethanidine showed loss of blood pressure control. 3 The metabolic clearance of antipyrine was unaltered in two subjects studied, showing no evidence of induction or inhibition of hepatic microsomal oxidizing enzymes by Ciba 34276-Ba.