A comparison has been made of insulin absorption rate and its variability in healthy subjects (n = 12), matched Type 1 diabetic patients (n = 12), and brittle Type 1 diabetic patients (n = 13) after subcutaneous injection with a standardized injection technique. In each individual 8 U of iodinated neutral human soluble insulin were injected twice, at the fat-muscle boundary. Disappearance of radioactivity was measured for 8 h. Differences in absorption rate could not be demonstrated (T50 207 +/- 30 (+/- SD), 224 +/- 73 and 217 +/- 80 min in the three groups, respectively). Intra-individual variance was similar in the three groups (intra-individual SD of T50 14 +/- 9, 10 +/- 6 and 12 +/- 10%, respectively). Injection with the skinfold technique each patient usually employed, did not alter mean absorption rate or its variability significantly (T50 179 +/- 52 min; intra-individual SD 12 +/- 8%). In a group of Type 1 diabetic patients (n = 26) the absorption rate after deep injection was compared with that after superficial injection. No differences were found (T50 207 +/- 66 vs 236 +/- 66 min). In some of these patients (n = 10) plasma free insulin and glucose concentrations were measured. The increase in free insulin concentrations was significantly different only at some time-points, but insulin curves and plasma glucose concentrations did not differ significantly. Thus neither insulin absorption nor its variability differ between healthy subjects and diabetic patients, between deep and superficial subcutaneous injection, or between stable and brittle diabetic patients.