For the study of the microcirculatory disturbance of the digestive tract in patients with diabetes, 41 cases with non-insulin dependent diabetes mellitus (NIDDM) were selected (mean age 53.9 Yrs., 22 male/19 female). Of these patients 9 were without complication, and 32 with complications. Gastric mucosal blood flow (GMBF) was determined at 14 points of laser and greater curvature, anterior and posterior wall of antrum, angle and corpus of stomach, pylorus and anterior wall of duodenum with laser Doppler flowmetry (PF2). Results showed that the mean value of the 14 points of GMBF in 41 patients with NIDDM was 2.81 +/- 0.15(V, mean +/- s mean), which was significantly lower than that of 11 normal subjects (4.77 +/- 0.29V, P < 0.001). The mean GMBF of 8 cases of NIDDM without gastric disease was 2.92 +/- 0.28V, which was also lower than that of normal control (61.2% of normal value, P < 0.001). The GMBF in 27 cases of diagnosed chronic superficial gastritis (CSG 2.79 +/- 0.15V) was lower than the GMBF of 63 CSG patients without NIDDM (3.23 +/- 0.12V, P < 0.05). The viscosity of blood and plasma was determined with NAAKE viscometer in 26 patients with NIDDM. It was found that the blood viscosity was significantly higher than that of the normal control, and the plasma viscosity was also increased but without statistic significance. Results showed that the GMBF of NIDDM was significantly lower than that of the normal subjects or CSG patients without diabetes. It implied that the visceral microcirculatory disturbance also involved the digestive system leading to the GMBF decrease.(ABSTRACT TRUNCATED AT 250 WORDS)