Evoked end-plate potentials (e.p.p.s) were recorded in phrenic nerve-hemidiaphragm preparations from rats which had been subjected to periods of dietary restriction. 2. The mean quantum content of the first e.p.p. of trains of e.p.p.s was significantly increased after 1 week of dietary restriction in 30-day-old but not in 110-day-old rats. 3. The mean quantum content of plateau e.p.p.s elicited at a frequency of 10 Hz was not significantly affected by brief periods of dietary restriction in either 30-day-old or 110-day-old rats. 4. In the younger animals there was found to be a decrease in the safety factor of neuromuscular transmission following dietary restriction when this parameter was calculated using previously reported values for the amplitude of spontaneous miniature end-plate potentials (m.e.p.p.s) after such a restricted diet. 5. Such rapid changes in neuromuscular transmission following brief periods of dietary restriction indicate that great care is required in the choice of adequate control animals when food intake is altered by experimental procedures.
