A significant association between N-ras oncogene activating point mutations and testicular cancer has recently been reported. We have studied DNA samples from the blood and fresh tumor tissues of 17 Norwegian testicular cancer patients (11 seminomas/6 nonseminomas). Point mutations in K-ras-2 and N-ras exons 1 and 2 were studied by denaturing gradient gel electrophoresis (DGGE) and by oligonucleotide hybridization. No N-ras mutations were detected in these tumor samples, but two K-ras-2 exon 1 mutations were found in two of the seminoma tumors (stage I and II tumors) using the DGGE technique. The mutations were confirmed by dot blotting and oligonucleotide hybridization and identified as a G-->T and a G-->A point mutation in K-ras-2 codon 12, leading to a valine and a serine substitution, respectively. All the white blood cell DNAs were negative. As a positive control for DGGE screening, we ran two plasmid constructs carrying human N-ras exon 2 sequences with mutations. To study the role of ras gene activation in testicular cancer, a larger tumor sample population will be investigated.