In canine cutaneous veins cooling augments and warming depresses the responses to sympathetic nerve stimulation. In these veins the extract of Ruscus aculeatus (Ruscus) causes contractions due to alpha-adrenergic activation. To determine the effects of temperature on the response to Ruscus, rings of canine saphenous veins were studied at 24 degrees, 37 degrees and 41 degrees C. At 37 degrees C, Ruscus caused an increase in isometric tension which was depressed by prazosin and rauwolscine. Cooling inhibited the response to Ruscus, while warming augmented it. Rauwolscine potentiated, and prazosin reversed the effect of cooling on contractions evoked by Ruscus. Prazosin reduced, and rauwolscine augmented the effect of warming. These experiments demonstrate that temperature affects the venoconstriction induced by Ruscus in an opposite fashion as that to sympathetic nerve activation, presumably because the alpha 1-adrenergic component of the response to Ruscus predominates.