Young rats were subjected to low-level, repeated doses of x-irradiation from a Co60 source and examined for the presence and arrangement of their GFAP-immunopositive system at the light and electron microscopic levels. In 2-week-old control rats, labelled cells were already distributed homogeneously throughout the bulb, while in the experimental animals, a (newborn- and early postnatal-type) radial arrangement of immunoreactive fibres continued to persist even until the end of the fourth postnatal week. This delay in the maturation of the GFAP-immunopositive glial system may contribute to the hindered development of the bulbar neurones, neuronal connections, and field potentials, as found in earlier studies.