Several different studies have investigated the growth effects of angiotensin II on vascular smooth muscle cells in culture. However, smooth muscle cells change their phenotype when placed in culture. The objective of the present study was to investigate the effects of angiotensin II on (3)H-thymidine and (3)H-proline incorporation in vascular smooth muscle cells in culture and in the tunica media of blood vessels perfused at normal physiological pressures in organ culture, thus avoiding the phenotypic changes observed in cell culture. The perfusion system consisted of a peristaltic pump and a closed circuit of plastic tubing connected to a culture media bottle where thoracic rat aortae were placed. Angiotensin II induced an increase in (3)H-thymidine and (3)H-proline incorporation in both culture systems. The results suggest that angiotensin II may play a role in mediating cell growth in vascular smooth muscle cells in their 'contractile' as well as in their 'synthetic' phenotype.