1. Some aspects of the pharmacology of neuromuscular transmission have been studied in the isolated diaphragm of the normal and dystrophic mouse. 2. The effects of (+)-tubocurarine and atropine on the indirectly elicited twitch responses of the dystrophic diaphragm were indistinguishable from normal. 3. Intracellular recording techniques revealed no significant differences between the rise time, time to half decay, frequency and amplitude of miniature endplate potentials (m.e.p.ps) recorded in dystrophic muscle fibres, compared to those recorded in normal muscle fibres. 4. Transmitter null potential, the size of the available store of transmitter, the probability of release of the transmitter, and the characteristics of endplate potentials (e.p.ps) of dystrophic muscle fibres did not differ from normal. 5. The quantum contents of e.p.ps generated in response to nerve stimulation of 0.1 to 100 HZ were consistently larger in dystrophic muscle fibres than in normal muscle fibres, but the differences were not statistically significant under the conditions of the experiment.