Miniature endplate currents (mepcs) were recorded in embryos and larvae of Drosophila melanogaster with the patch clamp technique in the whole cell configuration from abdominal ventral oblique muscles. Shortly after nerve-muscle contacts (16 h after egg laying) mepcs were small and infrequent. The mean amplitude of mepcs increased abruptly during late embryonic stages but did not change any further up to second instar larvae. The amplitude distribution of mepcs was skewed toward larger amplitudes and changed drastically to a more broader distribution at the time of hatching, but did not change any further. These muscle cells were found to be electrically coupled to those in the rostral neighbor segment. The synaptic current has a fast rising phase and decayed with a single exponential throughout the developmental period examined. The decay time constant increased with amplitude but the rise time did not. Neither the rise time nor the decay time constant changed with development. Many synaptic currents decayed in a stepwise manner revealing underlying single channel events. Two discrete steps were discerned, with amplitudes of about 7.6 and 16 pA at -60 mV. These two types of channels were observed throughout the stages examined.