In this study, 5-hydroxydopamine was used to help differentiate adrenergic and nonadrenergic nerve terminals in canine renal arteries. There were both adrenergic and non-adrenergic varicosities in the adventitia near the outer surface of the media. The adrenergic varicosities had accumulated 5-hydroxydopamine, were more numerous than the nonadrenergic varicosities, and were found in the media in close relation to smooth muscle cells.