Severe IDDM (insulin-dependent diabetes mellitus) was produced in the musk shrew (Suncus murimus, Insectivora) by a high dose (a single intraperitoneal injection of 100 mg/kg Body Weight) of streptozotocin (STZ) injection. All shrews that were administered a high dose of STZ exhibited hyperglycemia (449 +/- 16 mg/dl vs 73 +/- 4 mg/dl in controls) and hypoinsulinemia(0.25 +/- 0.07 ng/ml vs 10.96 +/- 1.97 ng/ml in controls) with ketosuria 10 days after injection. Their livers were enlarged and exhibited ayellowish-brown color with marked triglyceride (TG) accumulation (63.25 +/- 7.10 mg/g Liver vs 2.11 +/- 0.19 mg/g Liver in controls). It is probable that the increased influx of fatty acids into the liver induced by hypoinsulinemia and the low capacity of excretion of lipoprotein secretion from liver in the musk shrew resulting from a deficiency of apolipoprotein B synthesis play important roles in fatty liver formation. Hyperlipidemia was another feature in shrews with severe IDDM. The blood TG level was especially high in these shrews (899 +/- 178 mg/dl vs 23 +/- 5 mg/dl in controls). These results indicate that the IDDM shrew, induced by high doses of STZ, is a unique model characterized by fatty liver and hyperlipidemia and may be useful for studying lipid metabolism of IDDM.