1. Excitatory junction potentials (e.j.p.s) were recorded intracellularly in the guinea-pig vas deferens following stimulation of the hypogastric nerve. Differentiation of the rising phase of the e.j.p. showed them to be made up of transient peaks in the rate of depolarisation, the 'discrete events'. 2. In any one cell discrete events occurred at one or several latencies, intermittently, the frequency of occurrence varying between 1 in 1.8 to 1 in 45 stimuli. 3. Intermittence was not an artifact due to the use of submaximal stimulation nor the result of a ganglionic relay between the hypogastric and vas deferens nerve. 4. Discrete events occurring with a single latency had amplitudes that were multimodally distributed. In some cells the preferred values of amplitude were simple whole number multiples of the smallest preferred value. 5. The time course of discrete events varied from cell to cell and at different latencies. The discrete event had a time to peak of 5.3 +/- 1.9 msec, n = 220 (mean +/- S.D.) and a time to half decay of 8.3 +/- 3.6 msec, n = 220. 6. Discrete events in a cell could be matched for amplitude and time course by spontaneous excitatory junction potentials in the same cell and both probably represent the release of a single packet of transmitter. 7. The e.j.p. is made up of (1) discrete events which represent the release of transmitter from a single varicosity, (2) a non intermittent slow component which represents the electronic spread of activity from smooth muscle excited from distant release sites. 8. It is concluded that transmitter release from individual varicosities is packeted and the number of packets liberated per stimulus from a single varicosity is small, varying between zero and 10.