Recent evidence has suggested the presence of a malignant melanoma (MM)-related gene on human chromosome 9p21, the location of the putative tumour suppressor genes p15 and p16. DNA from patients with familial MM, from MM cell lines and sporadic MM cases has been examined for coding region and splice junction mutations of the p16 gene, but expression studies of both genes from the same cells have not been reported. We used the polymerase chain reaction to analyse p16 and p15 expression in 23 MM cell lines. Fourteen lines (61%) did not express either gene. Six (26%) expressed p16 and eight (35%) expressed p15. Expression patterns were concordant in most cases (83%), but one line (4%) expressed only p16 and three lines (13%) expressed only p15. These data suggest that loss of function of these genes, as judged by expression, may be higher than predicted by previous DNA-based studies. The lack of complete concordance between p15 and p16 expression implies that the genes are not functionally redundant and that loss of either gene may be important in the pathogenesis of MM.