We have already reported that slowly progressive non-insulin-dependent diabetes mellitus (NIDDM) is produced by a single i.p. injection of a subdiabetogenic dose (100 mg/kg) of streptozotocin (STZ) to 8-week-old male ICR mice. The aim of the present study was to clarify whether or not the progressive NIDDM is induced in ddY, BALB/c, C57BL/6 and ICR mice by the administration of STZ. Eight-week-old male mice of the 4 different strains were administered a single i.p. injection of STZ at various doses (ICR, ddY and BALB/c: 100—200 mg/kg; C57BL/6: 75—150 mg/kg). Among the ddY, BALB/c and C57BL/6 mice, a time course-related rise in non-fasting serum glucose levels throughout the observation period of 1—12 weeks after STZ administration was only induced in the 125 mg/kg STZ ddY and 100 mg/kg STZ ICR mice. In contrast with serum glucose levels, the area of islets and the percentage of the relative number of insulin-immunoreactive cells (β-cells) to glucagon-immunoreactive cells (α-cells) in the 100 mg/kg STZ ICR and 125 mg/kg STZ ddY mice continued to decrease gradually over time. In addition, in low dose STZ mice of both strains, the insulin response to glucose stimulation was extremely impaired over time, although non-fasting serum insulin levels were maintained near normal levels. The rate of the progression of diabetes was faster in the 125 mg STZ ddY mice than in the 100 mg/kg STZ ICR mice.