Transmission at an identified chemical synapse between two giant molluscan neurones, in the snail Achatina fulica, was sampled continuously from late embryogenesis to adulthood. The laboratory culture and reproductive life-cycle of the snail are described. The propagation of spontaneous excitatory postsynaptic potentials (Epsps) into the postsynaptic soma was documented throughout development. Short-term facilitation (Epsp(,2)/Epsp(,1)) was present at the identified synapse at all ages studied. Over a series of 100 trials, embryonic synapse showed a net synaptic depression; while, postembryonically, there was a progressive increase in frequency-facilitation with increasing age. A quantal analysis of transmission indicates that the amplitude of the quantal unit declines in parallel with the decrease in the postsynaptic input resistance. There is a progressive (20-fold) increase in quantal content from embryos to adults. The developmental increase in transmission at the synapse is primarily presynaptic in origin. Structural correlates for the electrophysiological findings were discussed.

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