Rabbit's isolated perfused aortic strips and hearts have been used to study the effects of diclofenac and pirprofen, non-steroidal antiinflammatory drugs (NSAIDs). Although diclofenac and pirprofen in concentrations ranging from 0.5-8 ug/ml and 12.5-100 ug/ml respectively had no effect on the resting tonus of the aortic strip preparations, yet both of them in the same concentrations produced a dose-related statist ically significant augmentation of adrenaline and noradrenaline induced contractions of the preparations, which were less evident in preparations isolated from reserpinized rabbits (0.1 mg/kg body weight S.C. reserpine for 10 successive days). These augmenting effects of both drugs were almost absent in denuded aortic strips, in which the intimal endothelial cells were removed. Diclofenac (1-16 ug/ml perfusion fluid) had no effect on the contractility of isolated perfused rabbit heart, but in a concentration of 50ug/m I perfusion fluid it exerted a positive inotropic effect, which was almost absent in specimens obtained from· reserpinized rabbits. Larger doses (200 ug/ml perfusion fluid) exerted a toxic cardio-inhibitory effect. Pirprofen exerted no effect on cardiac contractility in concentrations ranging from 2.5-800 ug/m) perfusion fluid.