Cannabinoids reduce neurotransmitter release from both central and peripheral nerve terminals, but the mechanisms by which this inhibition takes place in sympathetic nerve terminals, downstream of the receptors, is unclear. In this study, we investigated two aspects of cannabinoid signalling, using the vas deferens: (1) whether cannabinoids reduce the release of both cotransmitters from sympathetic nerves (noradrenaline and ATP); and (2) whether endogenous cannabinoids provide activity-dependent negative feedback of neurotransmission. Balb/c mice were killed by concussion and cervical dislocation; both vasa deferentia were removed. Longitudinal isometric contraction of each isolated mouse vas deferens was recorded in an organ bath, with trains of field stimuli (0.5 ms width; suprathreshold voltage; 10 pulses at 10 Hz) applied in pairs through ring electrodes at 120 s intervals. The noradrenergic component of contraction was measured in preparations pretreated with α,β-methylene ATP (1 μM); the purinergic component was measured in preparations pretreated with prazosin (100 nM). THC (100 nM) decreased the amplitude of the noradrenergic component of contraction, with a significant reduction at 30 min (36±9%, P < 0.005, n = 6), and maximal reduction after 70 min (52±9%, P < 0.005). In a cumulative concentration-response study (3 – 300 nM), THC had an EC₅₀ of 9 nM (95% CI, 3 – 23 nM). The CB₁ receptor antagonist AM251 had no effect upon the noradrenergic component (n = 6). To test whether endocannabinoids could be released from the tissue following field stimulation, trains of either 10 or 200 pulses (at 10 Hz) were applied as conditioning stimuli; AM251 had no effect on subsequent test stimuli (10 pulses; delivered 15 s after the train; compared with a solvent control; n = 6). Intriguingly, there was no effect of THC (100 nM) on the purinergic component of contraction (n = 7 vasa deferentia). In conclusion, we report that THC inhibits noradrenergic neurotransmission with an EC₅₀ of 9 nM, apparently without affecting the purinergic component; further work is required to confirm the latter observation. There appears to be neither an endogenous tone, nor release from the tissue upon electrical stimulation, of active endocannabinoids in the vas deferens.