A neuro-anatomical rat brain atlas was designed for potential use in (regulatory) developmental neurotoxicity testing. In this atlas, ten major regions, together composing the total brain, are defined and delineated using natural and artificial borders between regions: i.e. neocortex, limbie cortex, olfactory bulb, hippocampal formation, eallosal body, caudate putamen, amygdala and thalamus/hypothalamus. To validate the atlas, the volume of the regions was estimated by two independent investigators using stereology (Cavalieri principle). For validation a group of ten 22 day old male Wistar rats was used. Once the outcome of the validation study proved to be satisfactory in terms of inter-investigator variation and reproducibility, the usefulness of the atlas as a screening tool for developmental neurotoxicity testing was evaluated, using the effects of prenatal exposure to methylazoxy methanol (MAM) as a model (1, 2). MAM (7.5 mg/kg bw/day), a compound inhibiting cell division, was dosed to female rats from gestation days 13 to 15 when mainly the forebrain and hippocampus are in proliferation whereas the cerebellum is not as this region develops mainly after birth. Control animals received saline. Groups for analyses comprised offspring of both sexes aged 22 and 62 days, both control and MAM exposed F1-animals (n=10 litters/group; 1 rat/sex/litter; 8 groups). The brain atlas appears to be an adequate and efficient tool to study the normal and abnormal development of the rat brain; the regions defined according to this atlas can be demarcated easily and reproducibly. In line with the exposure schedule used, MAM showed a remarkable growth suppressing effect on the different brain regions except for cerebellum and medulla oblongata. This effect is more pronounced in the male than in the female rat brain. This is not surprising as also the normal development of brain morphology differed between the sexes, implying a different time window of development and, hence, a different window for maximal vulnerability for neurodevelopmental toxicity.