Micrencephaly is induced in rats by injecting their mothers with methylazoxymethanol acetate (MAM) during pregnancy. The areas of the brain most effected are the cerebral hemispheres showing marked reductions in both neocortex and limbic cortex. Rats with this chemically induced micrenecephaly exhibit species typical behaviors and reproduce successfully in restricted laboratory cage environments which may present no significant challenge to the survival of micrencephalic individuals. The purpose of this study is to examine the behavior of micrencephlic rats living in slightly crowded, free-ranging groups in large, complexly structured environments: survival in these environments requires the learning of complex behaviors, such as lever pressing for water. Our preliminary results show that, although the micrencephalic rats can survive in mildly stressful situation, they exhibit a drastic reduction in reproductive success. Only about 10 per cent of the pups in the first litters born to MAM treated rats survived, compared to over 80 per cent of the pups in the first litters born to control rats. Poor reproductive success of the micrencephalic parents is associated with poor maternal behavior, and high levels of disruptive aggressive behavior among males.