Field stimulation of isolated rat vas deferens preparations caused a twitch contraction followed by a slower phasic contraction. Exogenously applied ATP and noradrenaline caused rapid contractions and slowly developing contractions respectively. Pretreatment with phentolamine antagonised the phasic response to stimulation and the contraction to noradrenaline. Pretreatment with AMP antagonized the twitch response to stimulation and concentrations to ATP. The results support the view that ATP is released as a co-transmitter with noradrenaline in sympathetic nerves.