Normal adult rat glial (RG) cells in culture have been shown to restrict rubella virus (RV) replication, permitting the synthesis of only five of the seven intracellular viral polypeptides associated with a normal, productive infection. Recently uninfected RG cells have been reported to differentiate into mature glia in the presence of dibutyryl cyclic AMP (dB-cAMP), suggesting that the RG cells may be a continuous cell line of undifferentiated glioblasts. This communication describes the effect of dB-cAMP on rubella-infected RG cells. Following exposure to dB-cAMP, RV antigens could be demonstrated in the cytoplasm of the differentiating glioblasts, all seven intracellular RV polypeptides could be detected following immune precipitation, slab gel electrophoresis, and autoradiography, and infectious progeny virions could be titered from the tissue culture medium. These data indicate that dB-cAMP promotes glioblast maturation and a concomitant activation of RV replication.