The effect of vasoactive agents on the spontaneous contractions of the initial lymphatics of the bat’s wing was investigated. Initial lymphatic contractile frequency and pulsatile pressure were measured with the servo-null micropressure system. Norepinephrine, phenylepinephrine, isoproterenol, acetylcholine, histamine, serotonin, bradykinin, prostaglandin F2a, prostaglandin E2, indomethacin and ibuprofen were delivered to the immediate vicinity of the initial lymphatic by microinjection or iontophoresis. Only bradykinin produced changes in initial lymphatic contractions which were significantly different from control. The response to bradykinin was characterized by an increase in the frequency, strength or duration of the contractio