The absorption of isophane(NPH) insulin (Human Insulatard) from palpably abnormal thigh insulin injection sites was determined in 10 C-peptide negative diabetic patients. Absorption was compared with a control day study when the insulin was injected into normal thigh. Standard meals were given 30 and 240 min after the injection. Within 2 weeks the tissue morphology and adipose tissue depths at both injection sites were assessed by ultrasound scanning. Absorption of isophane(NPH) insulin was markedly defective from the abnormal compared with the normal injection sites (area under the free insulin curve to 10 h 115 +/- 15 vs 188 +/- 21 mU l-1 h; p less than 0.01). The area under the blood glucose curve from 270 min to the end of the study at 600 min was significantly greater after injection into the palpably abnormal injection site compared with normal thigh (80.4 +/- 5.2 vs 61.2 +/- 7.0 mmol l-1 h; p less than 0.05) representing a 22% improvement in blood glucose control on the normal injection site afternoon. The depth of abnormal injection site tissue was significantly greater than the depth of adipose tissue at the control site (17 +/- 6 vs 5 +/- 4 mm; p less than 0.001) and considerable disruption of the normal anatomy observed. These results demonstrate defective absorption of isophane(NPH) insulin from palpably abnormal injection sites and describe the morphology of the abnormal tissue.