The putative gliotoxic compound, alpha-aminoadipic acid (AAA), has previously been reported to be a glial-selective toxin exerting its effects both in vivo and in vitro. This study sought to examine the effects of this compound on adult rat hippocampal astrocytes in vivo. Fourteen adult male Sprague-Dawley rats were injected with high concentrations of either the L-isomer or the racemic mixture of AAA into the dorsal hippocampal formation or corpus striatum. The animals were allowed to survive for times ranging from 4 to 48 h and the possible toxicity of the acid on astrocytes was monitored by glial fibrillary acidic protein (GFAP) immunocytochemistry. In every case, the GFAP-positive cells at the level of the injection site appeared identical, both in morphology and cell density, to control preparations. Based on our results, we conclude that AAA is not toxic to adult rat hippocampal astrocytes in vivo, nor could we confirm previous reports of toxicity to striatal astrocytes.