Although the WT1 gene has been implicated in the aetiology of Wilms' tumour, mutations in WT1 are found only in minority of the tumours. DNA methylation of regulatory elements represents another possibility of modulation of gene expression. We studied methylation in the promoter and enhancer regions of the WT1 gene in 34 Wilms' tumour patients by the polymerase chain reaction on HpaII-digested DNA and by the bisulphite method. No methylation was detected in the promoter region in either tumour or normal kidney or blood DNA samples. In contrast, a HpaII site in the enhancer region was at least partially methylated in normal kidney and blood DNA samples and in about one-third of the tumours, while the majority of tumours showed no methylation. The differential methylation in the enhancer region of the WT1 gene may indicate that methylation of this element can play a role in the regulation of this gene.