Glutathione transferase mu activity, a marker for susceptibility to lung cancer and chemically induced cytogenetic damage, is not a predictive index for the predisposition to sulphonamide hypersensitivity reactions. However, considering the functional diversity and broad, overlapping substrate specificity of GSH-dependent enzymes, it is conceivable that an as yet unidentified deficiency in another GST isozyme or GSH-related enzyme may be a marker for sulphonamide toxicity. In addition, heterogeneity in cellular repair mechanisms and the diversity of the human immune response [22] may also contribute to the manifestation of the toxic effects of sulphonamides. Experiments are currently in progress to determine which of this myriad of variables is predominantly responsible for inter-individual susceptibility to the idiosyncratic reactions produced by these antibacterial agents.