Two cDNA clones (lambda E1 beta 1, 1469 bp; lambda E1 beta 12, 1437 bp) encoding the beta-subunit of the pyruvate dehydrogenase (E1) component of the human pyruvate dehydrogenase complex were isolated from a human liver lambda gt11 cDNA library. The composite human liver E1 beta cDNA encoded the entire mature E1 beta [329 amino acids (aa)] as well as a portion (26 aa) of the E1 beta leader peptide. Significant discrepancies were identified between the nucleotide and deduced aa sequences of human liver E1 beta cDNAs and the corresponding sequences of a previously reported cultured human foreskin fibroblast E1 beta cDNA [Koike et al., Proc. Natl. Acad. Sci. USA 85 (1988) 41-45]. The composite human liver E1 beta cDNA generated in this study provides a reference sequence for investigating the structure-function relationship of human E1 beta and for characterizing genetic mutations in patients with E1 deficiency.