1,3-Butadiene (BD) is a rodent carcinogen that is bioactivated to at least two genotoxic metabolites, 1,2-epoxybutene (EB) and 1,2,3,4-diepoxybutane (DEB). The mutational spectrum for DEB at hprt in human TK6 lymphoblasts (TK6 cells) was determined and compared with the mutational spectrum from spontaneous mutants. A DEB exposure of 4 microM for 24 h resulted in an average 5-fold increase in the hprt mutant frequency. Hprt mutants for molecular analysis were isolated from TK6 cells exposed to 4 microM DEB for 24 h (51 DEB-induced mutants) and from a set of spontaneous mutants (n = 43) isolated from the same TK6 stock cell cultures. Molecular analyses of hprt mutations were done by reverse transcription-polymerase chain reaction (RT-PCR) of hprt mRNA or exon-specific genomic PCR amplification of hprt followed by DNA sequencing of PCR products. There was an increased frequency of A:T-->T:A transversions among the DEB-induced mutants compared to spontaneous mutants (9/51; 18% DEB-induced compared to 2/43; 5% in spontaneous (one-way Fisher's exact test; P < or = 0.05). DEB-induced hprt mutants also had an increased frequency of genomic deletions affecting the 5' region of hprt (7/51; 14% DEB-induced compared to 1/43; 2% in spontaneous). Therefore, DEB is a mutagenic carcinogen that can induce genotoxicity by large deletions, rearrangements or single base substitution mutations.