OBJECTIVE To assess whether laser Doppler flowmetry could detect differences in the cutaneous response to postischemic reactive hyperemia between patients with non-insulin-dependent diabetes mellitus (NIDDM) and nondiabetic controls and among subgroups of NIDDM patients. METHODS We measured the cutaneous blood flow on the forearms during the postischemic reactive hyperemia test in diabetic patients and nondiabetic controls. Subjects were 25 patients with NIDDM from the outpatient clinics of dermatology, ophthalmology, and endocrinology and 25 nondiabetic volunteers matched for sex and age. Of the patients with NIDDM, 14 had proliferative retinopathy, and 13 were obese. Cutaneous postischemic reactive hyperemia test monitored by measuring the cutaneous blood flow with laser Doppler flowmetry was used. Peak blood flow (P) after arterial occlusion, the time required to reach this peak (Tp) and the ratio (K) between these two quantities (K = P/Tp) were measured. RESULTS In diabetic patients, P was significantly lower (P less than 0.02) than in nondiabetic control subjects. In diabetic patients with proliferative retinopathy, K was lower (P less than 0.05) than in diabetic patients without retinopathy. Diabetic patients with a body mass index (BMI; wt/ht2) less than 25 kg/m2 had a longer Tp (P less than 0.002), whereas the control group BMI did not affect this parameter. The combination of retinopathy and BMI less than 25 gave the longest Tp values (P less than 0.0001). CONCLUSIONS Postischemic hyperemia tests in diabetic patients reveal cutaneous microcirculatory changes in the forearm (lower P). Advanced retinopathy is associated with functional disturbances (lower K), especially when combined with a low BMI (less than 25; longer Tp).