Side effects of perinatal exposure to L-aspartyl-L-phenylalanine methyl ester (aspartame [ASP]) were studied by providing ASP-containing water to female rats from 30 days before conception until the pups were 30 days of age. Compared with pups of mothers who drank plain water, ASP-exposed pups were not different in morphological (pinnae detachment, eye opening, incisor eruption, and body weight) and reflex (surface righting and negative geotaxis) development. No difference was found in the time taken by mothers to retrieve litters. At 30 days of age, performance of ASP-exposed Ss in a radial-arm maze differed from that of Ss not exposed. Results suggest that ASP may either facilitate the development of components involved in this procedure or reduce factors that interfere with this task.