The NG108-15 and C6 cell lines were used in the present study as neuronal and glial models, respectively, to examine the cytotoxicity of the major metabolite of cocaine, benzoylecgonine (BE). Exposure of both cell types to varying concentrations of BE resulted in a loss of cells from the growth surface. Analysis of the unattached cells after such exposure, using a variety of techniques, revealed that these cells were not viable. Therefore, this effect could not be ascribed to BE interfering with cell-substratum interactions. The early events in BE cytotoxicity were examined by observing cells cultivated on the stage of an inverted microscope, using differential interference contrast (Nomarski) optics. Upon exposure of either cell type to 10 microM BE a retraction of cellular processes could be observed within 30 min. Within 6 h cell death was apparent. Similar analyses using 50 microM BE in the growth medium resulted in similar results, except that process retraction could be observed as early as 15 min after exposure. These results demonstrate that the major metabolite of cocaine, benzoylecgonine, is cytotoxic to in vitro models of neuronal and glial cells.