BACKGROUND: There have been several reports about insulin secretory impairment in non-obese type 2 diabetic patients and even in impaired glucose tolerant subjects in Korea. Insulin secretory impairment might be induced by insufficient beta-cell mass, functional defects of beta-cells or both. To clarify the cause of impaired insulin secretion in type 2 non-obese diabetic patients in Korea, beta- cell masses were quantified in normal and type 2 diabetic subjects. METHOD: Normal pancreases were procured by 6 heart-beating non-diabetic donors under informed consent from relatives and approval of the university ethical committee. To quantify the beta cell mass and insulin content in various part of the pancreas, first we divided it into 3 parts: head, body and tail, and then each three parts were weighed and subdivided again into 8 segments equally. For diabetic patients, tissue sections were obtained from 15 partial or total pancreatectomized type 2 diabetic patients of any causes. After being fixed, tissues were immunostained using the Streptavidin-biotin-peroxidase method with anti-insulin antibody. Beta cells were counted by point count method. RESULTS: The mean value of total pancreas weight of normal subjects (n=6) was 77.1+/-14.6 g, that of mean relative volume of beta cells in the pancreas was 2.1+/- 0.9%, ranging from 1.4% to 3.1% (head 2.3+/-0.6%, body 1.8+/-0.2%, tail 2.2+/-0.4%). Mean value of total beta cell mass which was calculated from relative volume of beta-cells and weight of each portions was 1.3+/-0.3 g, ranging from 1.2 g to 1.9 g (head 0.6+/-0.3 g, body 0.4+/-0.2 g, tail 0.4+/-0.2 g). Mean insulin content per pancreas was 63.6+/-46.6 g, ranging from 27.8 to 137.2 g/pancreas (head 25.1+/- 19.1 g, body 20.8+/-15.5 g, tail 17.7+/-14.9 g). In diabetic patients, relative volume of beta cells in tissues were variable from 0.4% to 2.8% and there was good correlation between beta-cell mass and body mass index of the diabetic patients. However we can't find the correlation among relative volume of beta-cell, (r2=0.55, p<0.05) duration of diabetes and age. Remarkable heterogeneity for loss of beta-cells in the islets of diabetic patients was observed even in the same lobe of pancreas. There were no evidence of lymphocytic infiltration in the islets. CONCLUSION: Insufficient beta cell mass seems to be a main cause for insulin secretory impairment in non-obese type 2 diabetic patients in Korea.