Tumour necrosis factor alpha (TNF-alpha) appears important in ultraviolet-induced immunosuppression, suggesting that it is a susceptibility candidate for cutaneous basal cell carcinoma (BCC). We now describe data on the association between TNF microsatellite polymorphisms, first on susceptibility in 202 controls and 133 cases each having two to 30 BCCs, and secondly, within the cases, on BCC numbers. The data show that the proportions of individuals with TNF a1- and a7-containing genotypes were significantly different (P = 0. 0271, P = 0.0393, respectively) between cases and controls. Secondly, within the cases, TNF alleles d4 (P = 0.023) and d6 (P = 0.006) alone, and the TNF a2-b4-d5 haplotype (P = 0.007), were significantly associated with the number of BCC lesions. These preliminary data provide the first evidence that TNF microsatellite polymorphism may influence the pathogenesis of multiple BCC.