The limited effectiveness of cognitive behavioural marital therapy (CBMT) for some couples may be due to a failure to achieve generalized changes in behavioural, cognitive or physiological responses during marital interaction. In the present study an intra-subject replication design across five maritally distressed couples assessed changes associated with CMBT in behaviour, cognitions, and physiological arousal during marital communication. These response domains were assessed weekly in both clinic and home settings. Introduction of CBMT was associated with clear reductions in behavioural negativity in both settings for all couples, some variable cognitive changes across couples and settings, but no consistent change in physiological arousal across couples or settings. Physiological responding was asynchronous with behaviour and cognition. Further research is needed on the significance of physiological arousal in marital distress, and the importance of changes in physiological responding during marital interaction to marital therapy outcome.