In man, total glucose uptake is the sum of insulin mediated glucose uptake and non-insulin mediated glucose uptake. The later pathway has not been examined in Type 1 (insulin-dependent) diabetes mellitus. In order to assess non-insulin mediated glucose uptake in Type 1 diabetes, we measured steady-state rates of glucose uptake during glucose clamps at 5.27, 9.71 and 12.5 mmol/l using low (0.25 mU.kg-1.min-1), intermediate (0.75 mU.kg-1.min-1) and high (1.50 mU.kg-1.min-1) insulin infusion rates in 10 subjects with Type 1 diabetes. For insulin infusion rates of 0.25, 0.75 and 1.50 mU.kg-1.min-1 as plasma glucose rose from 5.27 to 9.71 mmol/l, total glucose uptake increased by 35, 43 and 52 percent respectively (p less than 0.05 for each insulin infusion rate). For all three insulin infusion rates, there was no significant increase in total glucose uptake as plasma glucose increased from 9.71 to 12.5 mmol/l. At each glycaemic level, glucose uptake correlated significantly with plasma free insulin (r = 0.81, p less than 0.01 at 5.71 mmol/l; r = 0.84, p less than 0.01 at 9.71 mmol/l; r = 0.73, p less than 0.02 at 12.5 mmol/l). Linear regression analysis to a point corresponding to plasma free insulin equalling zero, yielded values for non-insulin mediated glucose uptake (mmol.kg-1.min-1) of 0.11, 0.14, 0.18 at plasma glucose of 5.27, 9.7 and 12.5 mmol/l respectively. Thus, increasing plasma glucose concentrations were associated with increasing rates of non-insulin mediated glucose uptake. For each insulin infusion rate used, the percent of total glucose uptake accounted for by non-insulin mediated glucose uptake remained independent of plasma glucose concentration, but decreased as insulin infusion rate increased.(ABSTRACT TRUNCATED AT 250 WORDS)