An attempt at an analysis of the factors determining the time course of the end-plate current. I. The effects of prostigmine and of the ratio of Mg 2+ to Ca 2+ .

1. An attempt was made to analyse the factors which might determine the time course of the falling phase of the end-plate current.2. The end-plate current was measured by ;clamping' the membrane potential during neuromuscular transmission.3. The falling phase of the end-plate current was found to consist of a non-exponential, and an exponential portion, the duration of both of which varies under different experimental conditions.4. The results suggest that the rate constants determining the dissociation of the receptor-mediator complex seem greatly to influence the time course of the end-plate current.