The hormonal (growth hormone, glucagon, cortisol) and metabolic (glucose, ketone bodies) responses to 30 min of continuous vs 30 min of intermittent exercise were evaluated in five male children with insulin-dependent diabetes mellitus (IDDM) and five healthy male children. Each subject performed both types of exercise. In the healthy children, growth hormone levels rose, and glucose, glucagon, cortisol, and ketone bodies remained unchanged during both continuous and intermittent exercise. In the IDDM subjects, the mean reductions in glucose concentration were 99 mg% and 84 mg% during continuous and intermittent exercise, respectively. The levels of cortisol and ketone bodies in the IDDM subjects were significantly (P less than 0.05) elevated above the values obtained in the healthy subjects irrespective of the type of exercise. The mean concentrations of growth hormone, glucagon, cortisol, and ketone bodies were not significantly different between continuous and intermittent exercise. The study concludes that in healthy children the hormonal and metabolic responses to a continuous and an intermittent exercise protocol are similar. In the IDDM subjects, however, both forms of physical activity are associated with a decline in plasma glucose and no significant differences in hormonal and metabolic responses.