The TRE17 oncogene, originally cloned from transfected DNA of Ewing's sarcoma cells, maps to chromosome 17q and is expressed in a wide variety of human cancer cells. We recently detected the variants of this gene by using the polymerase chain reaction (PCR) and sequencing from the first exon to the third intron. Based on sequence homology scores, the variants could be grouped into three families, denoted alpha, beta, and gamma. Here, we used human keratinocytes from healthy skin which had been spontaneously immortalized and then rendered malignant by serum privation in vitro. Both immortalized and malignant cells expressed TRE17 sequences to the same extent, and, according to the restriction site analysis of cloned PCR products, both contained common and rare TRE17 variants in similar proportions. These variants, one of each from both cell types, were then sequenced and compared with those from the previous study. In the phylogenetic tree, they clustered with alpha and gamma at the most distant tree positions. The overall fraction of conserved sites in the whole TRE17 repertoire was 80%. An unexpected feature of the observed variability was that intronic sites were significantly better conserved than exonic sites. Members of TRE17 gamma detected in immortalized and malignant keratinocytes differed one from another, and both differed from the TRE17 gamma already identified in Ewing's sarcoma. No TRE17 gamma has been found so far in healthy tissues, thus leaving open the possibility of its origin from TRE17 beta by somatic changes during tumor progression.