We examined the relative efficacy of two modes of insulin therapy in five patients with insulin-dependent diabetes. Using a crossover protocol, therapy with multiple insulin injections was compared with the use of continuous subcutaneous insulin infusion (pump therapy); both therapies were regulated by home blood glucose monitoring. Although both therapies were equally effective during 2 to 4 days of inpatient management, pump therapy was clearly superior in the outpatient setting. Mean plasma glucose and hemoglobin A1c concentrations and the frequency of hypoglycemic reactions were significantly less with pump therapy despite apparently equal compliance with both therapies. We conclude that in compliant adult patients with type I diabetes continuous insulin infusion is more effective in achieving normalization of plasma glucose concentration than intensified conventional therapy in the outpatient setting. Although these patients found pump therapy preferable to intensive conventional therapy, the superiority of pump therapy is not explained by this bias. Whether these results are applicable in a more standard treatment setting remains to be established.