Loss of heterozygosity (LOH) studies have suggested that somatic mutations of a tumour suppressor gene or genes on chromosome 3p are a critical event In the pathogenesls of non-familial renal cell carcinoma (RCC). Germllne mutations of the von Hippel — Lindau (VHL) disease gene predispose to early onset and multifocal clear cell renal cell carcinoma, and the mechanism of tumorigenesls In VHL disease is consistent with a one-hit mutation model. To Investigate the role of somatic VHL gene mutations in non-familial RCC, we analysed 99 primary RCC for VHL gene mutations by SSCP and heteroduplex analysis. Somatic VHL gene mutations were Identified In 30 of 65 (46%) sporadic RCC with chromosome 3p allele loss and one of 34 (3%) tumours with no LOH for chromosome 3p. The VHL gene mutations were heterogeneous (17 frameshift deletions, eight missense mutations, four frameshift insertions, one nonsense and one splice site mutation), but no mutations were detected in the first 120 codons of cloned coding sequence. Most RCCs with somatic VHL mutations (23 of 27 (85%) informative cases) had chromosome 3p25 allele loss in the region of the VHL gene so that both alleles of the VHL gene had been inactivated as expected from a two–hit model of tumorigenesis. Detailed histopathology was available for 59 of the tumours investigated: 18 of 43 (42%) RCC with a clear cell appearance had a somatic VHL gene mutation but none of 16 non–clear cell RCC (eight chromophilic, three chromophobe and five oncocytoma) (x²= 7.77, P<0.025). These results suggest that somatic mutations of the VHL gene are a critical event in the pathogenesis of non-familial clear cell renal carcinoma, but do not exclude a role for other chromosome 3p tumour suppressor genes.