The cytotoxicity of irritants on human oral and skin keratinocyte culture models was compared. Keratinocytes were exposed to sodium lauryl sulphate and benzalkonium chloride at concentrations of 10(-4)-10(-7) M for 24 h. Cytotoxicity was evaluated by changes in mitochondrial metabolic activity (MTT assay) and plasma membrane integrity (LDH leakage). Our results showed that oral and skin keratinocytes are equally sensitive to the irritants tested. There were marked similarities in susceptibility between each cell type cultured from six individuals. The immunohistochemical staining pattern of both cell types resembled that of the basal cell. These observations suggest that the skin keratinocyte culture model may be useful in evaluating the cytotoxicity of agents which are irritants on either the skin or oral mucosa.