In recent years attention has been focused on HDL-Cholesterol (HDL-C) as a possible antiatherogenicfactor. Many investigators have reported a variety of plasma HDL-C levels in diabetesmellitus of humans and animals. The aim of this study was to define such changes of plasma HDL-C level in spontaneously diabetic and aged non-diabetic Chinese hamsters. The Chinesehamsters in the Asahikawa colony (CHA) were divided into three groups; a non-diabetic group (n=76, 7.9±0.2M, FPG 62 ± 2mg/dl), a diabetic group (n=39, 8.0± 0.3M, FPG 416 ± 9mg/dl) and anaged non-diabetic group (n=18, 25.3 ± 0.6M, FPG 85 ± 5mg/dl). Plasma HDL-C was measuredby μl-scale ultracentrifugation using an RPL-42T rotor (Hitachi). The total plasma lipoproteinpatterns in the non-diabetic and diabetic hamsters were analysed by gradient gel (PAA 2/16, Pharmacia) electrphoresis. The results obtained were as follows;<BR>1) The diabetic hamsters had hypoinsulinemia and hyperlipidemia.<BR>2) Plasma HDL-C levels in the diabetic hamsters were significantly elevated as compared withthose in the non-diabetic hamsters.<BR>3) A significant positive correlation between plasma HDL-C level and total cholesterol level wasobserved in the non-diabetic and diabetic hamsters.<BR>4) The male hamsters tended to have more elevated HDL-C and total cholesterol levels than thefemale hamsters.<BR>5) Electrophoretic analysis showed that plasma LDL scarcely existed in the Chinese hamsters andthat plasma VLDL, LDL and HDL increased in the diabetic hamsters. Furthermore, ultracentrifugalanalysis showed that plasma chylomicron appeared only in the diabetic hamsters.<BR>6) The apparent average molecular weight of HDL from the Chinese hamster estimated by gradientgel (PAA 4/30, Pharmacia) electrophoresis was approximately 265, 000. Moreover, it was shownthat the HDL particle was heterogenous. There was no difference in the average molecularweight and the particle distribution of HDL between diabetic and non-diabetic hamsters.<BR>7) Plasma HDL-C, total cholesterol, FPG and blood lipoperoxide levels were elevated with ageing.<BR>The finding that plasma HDL-C level was elevated in spontaneously diabetic and old non-diabeticChinese hamsters is thought to be of considerable interest since such changes of plasma HDL-Chave not yet been clarified in diabetes mellitus of humans. Further studies will be required todetermine the mechanism of elevation of plasma HDL-C in these animals.