The use of primary cultures of astrocytes as indicators of toxic potential was assessed using 20 selected compounds. Multiple endpoints were used to evaluate astrocyte reactions. Trypan blue dye exclusion and total cellular protein content of the cells were used as general indices. EC(50) values from the trypan blue experiments could be used to rank toxicity of compounds in a manner that correlates well with known toxicity for compounds that have specific astrocyte toxicities. Neurone specific neurotoxicants had no measurable effects on astrocytes indicating that this system differentiates gliotoxicity from neurotoxicity. Protein content, and content of the astrocyte specific glial fibrillary acidic protein (GFAp), were seen to increase at lower doses of gliotoxic compounds. This phenomenon appears to be similar to reactive gliosis in vivo, as assessed by immunostaining, and is an extremely sensitive indication of cellular damage. Support studies using astrocyte uptake of 2-deoxy glucose showed a similar pattern of activation in the cells as protein increases. This has been confirmed using the nonisotopic technique of MTT reduction.