The possible involvement of cyclic AMP in the stimulation-evoked 3H-overflow from rabbit isolated ear artery preloaded with 3H-noradrenaline was studied. Cyclic AMP (10(-5)-3 x 10(-4)M), 8-bromo-cyclic AMP (3 x 10(-4)M) and adenosine (10(-5)-3 x 10(-4)M) enhanced stimulation-evoked 3H-overflow. Dibutyryl-cyclic AMP (10(-5)-3 x 10(-4)M) had no effect. Theophylline (3 x 10(-5)M) and the phosphodiesterase inhibitor AH 21-132 (3 x 10(-5)M) did not alter the enhancement of 3H-overflow caused by either cyclic AMP or adenosine. Forskolin (3 x 10(-6)M) and the phosphodiesterase inhibitors ICI 63 197 (10(-4)M) and AH 21-132 (3 x 10(-6)-3 x 10(-5)M) increased stimulation-evoked 3H-overflow. Forskolin (10(-6)M) enhanced the effect of ICI 63 197 (3 x 10(-5)M) but it did not alter the effect of AH 21-132. It is concluded that cyclic AMP is involved in the stimulation-evoked release of noradrenaline from postganglionic sympathetic nerves in the rabbit ear artery.