Spontaneous isometric contractions and field-evoked responses were recorded in vitro from strips of bovine mesenteric lymph node capsule. Field stimulation (0.3 ms pulses, 60 V nominal, 2 min trains) at frequencies > or = 2 Hz evoked a frequency-dependent increase in baseline tension which was maximum at frequencies > or = 16 Hz. Evoked contractions were significantly reduced (P = 0.02) by the neurotoxin tetrodotoxin (10(-6) M) although they were unaffected by the alpha-adrenoceptor antagonists phentolamine, rauwolscine and prazosin (3 x 10(-6) M). Similarly, responses were unaffected by the beta-adrenoceptor antagonist propranolol (10(-6) M), the cholinergic antagonist atropine (10(-6) M) or the uptake blocker cocaine (10(-6) M). Field-evoked contraction was also unaffected by a 30 min exposure to alpha,beta-methylene ATP (10(-6) M). The results suggest that bovine lymph node capsular smooth muscle is innervated by excitatory nerves which are non-adrenergic, non-cholinergic and non-purinergic in nature.