Miniature end-plate currents (mepcs) were recorded from fast and slow muscle fibres in two muscles, m. cruralis and m. ileofibularis, under voltage clamp or extracellularly. Both fibre types showed an identical sensitivity to α-bungarotoxin, and an exponential dependence of mepc decay time-constant upon membrane potential, but there were some important differences: i) the rise time and half-time of decay were approximately 3 times longer in slow junctions than in fast ones: ii) inhibition of AChE had a more prominent effect on mepcs recorded in fast fibres while preserving the significant difference in mepc time course between fast and slow fibres; iii) treatment by α-bungarotoxin had a greater effect on mepc time course in slow junctions even in the absence of anticholinesterase; iv) a more prominent variability of mepc time course was observed in slow junctions, especially after treatment by anticholinesterase drugs.