A new method is presented for the quantification of cell viability based on densitometry with computerized image analysis. Neuronal cells were stained with crystal violet and densitometric analysis was performed with an IBAS 2.0 image analyzer (Kontron/ Zeiss), using specially implemented dedicated software which integrates the optical density of the culture in each well with the area covered by the stained cells. To test the reliability of the densitometric method cortical cells were plated at different concentrations (5 x 10(4)-10(6)/ml); the standard curve obtained by analysis of crystal violet staining showed a linear proportion between cell number and optical density signal. The validation and accuracy of the method were assessed and compared with other methods using rat cortical cells cultured in vitro for 10 days and exposed to kainic acid (250 microM) for 24 h. Neuronal viability was reduced by 40-50% and comparison with direct cell counting, MTT assay, and spectrophotometric analysis confirmed that the method is simple, quick, and reliable.