Twenty-four hour insulin requirements were measured in 5 uraemic insulin-dependent diabetics using a glucose controlled insulin infusion system (artificial endocrine pancreas). All patients were studied twice: initially 14 (1-27) days before institution of dialysis treatment and again after a mean of 46 (21-98) days on chronic dialysis therapy. At near normal blood glucose level the daily insulin requirements decreased from 44.8 +/- 2.9 U pre-dialysis to 35.0 +/- 2.3 U post-dialysis (P less than 0.001). The reduction included the prandial as well as the basal requirements. Consistent with this, the mean plasma free insulin level was higher pre-dialysis than post-dialysis (42 +/- 12 microU/ml vs 31 +/- 7 microU/ml) especially during daytime (49 +/- 11 microU/ml vs 37 +/- 9 microU/ml, P less than 0.03), suggesting that a decreased insulin degradation was not a major factor in the difference in insulin requirements. The effect of an acute change in azotaemia on insulin requirements was also evaluated in 4 uraemic diabetics on chronic haemodialysis the day prior to and the day after a routine dialysis (serum creatinine 922 +/- 59 mumol/l vs 555 +/- 109 mumol/l). No difference in insulin administration on the two days was observed (42.5 +/- 6.1 U vs 43.2 +/- 5.6 U). It is concluded that insulin resistance is present in uraemic insulin-dependent diabetics analogous to the insulin resistance widely prevalent in non-diabetic uraemic patients. The abnormality is at least partly reversible after several weeks on chronic dialysis, but not acutely. The pathophysiologic mechanisms underlying the insulin resistance in uraemia in the diabetic remain to be clarified.