The effect of paraquat (PQ, 1,1＇-dimethyl-4,4＇-bipyridium) on the histogene-sis and glycoconjugates (GCs) properties of the pyloric region of the stomach in a perinatal rat was examined by histological and histochemical methods. Oral administration of PQ (9 mg/kg per day in 0.2 mL of D.W.) on 7 to 14 days of gestation revealed growth retardation with significant reductions in the length of pyloric gland and their pit. As for histochemical properties of GCs in the pyloric region of the stomach, the PQ-treated rats showed some differences, such as delayed initial appearance of the sulfated GCs and lectin affinities compared with the vehicle group. These different GCs properties in the surface and gastric pit were usually detected in the fetal rats and more prominent and evident differences were revealed in the gland epithelium of the early postnatal rat. These results suggest that maternal PQ administration causes intrauterine growth retardation asso-ciated with delayed histogenesis and GCs immaturation of pyloric mucosa in developing rat.