The GSTM1 gene on chromosome 1p encodes the carcinogen-detoxification enzyme, glutathione S-transferase (mu subclass). The homozygous null genotype at this locus has been associated with increased susceptibility to malignancy, including some skin cancers. One hundred and twenty-four Australian patients with sporadic melanoma and 62 with familial basal cell carcinomas (a feature of nevoid basal cell carcinoma syndrome, NBCCS) were examined for germline homozygous deletions of GSTM1 using multiplex polymerase chain reactions. The homozygous null genotype was not overrepresented in either those with a single melanoma or in the NBCCS cases. Nor did it significantly accelerate tumorigenesis in either group. Analyses of much larger sample sizes will be required to investigate the representation of the null genotype in patients with multiple melanoma primaries and in those with melanoma co-existing with other non-cutaneous malignancies.