Increased survival of presynaptic-like neuronal profiles was found in cell cultures of rat cerebellum when the non-neuronal cell numbers were reduced with an antimitotic drug. In both treated and untreated cell cultures, neurites grew onto the polylysine-coated surface of sepharose beads and formed a swelling. The neuronal swelling contained an accumulation of synaptic vesicles and a membrane density at the site of contact with the bead and was called an apparent presynaptic element. The apparent presynaptic elements in untreated cultures increased in number from the time the beads were added to the culture to 7 days incubation and then showed a decrease to one half the 7-day value at 14 days incubation. A 75% reduction in cell division of non-neuronal cells was seen in cultures exposed to a 5 × 10-6 M cytosine arabinoside (Ara-C) for 2 days. Adding polylysine-coated beads to cultures treated with Ara-C showed at 14 days incubation a 7-fold increase in the number of apparent presynaptic elements as compared to untreated cultures. Additional experiments examined the numbers of neurites on the beads and found only small differences between treated and untreated cultures. A decrease, however, was shown in the number of glial fibrillary acidic protein staining astrocytes on the surface of the beads in treated cultures. The reduction of astrocytes by Ara-C appeared to enhance the survival of apparent presynaptic elements but did not enhance the growth of neurites. These results suggest that proliferating non-neuronal cells at a site of injury in the central nervous system may inhibit the formation of synaptic contacts and the growth of neurites through the site of injury.