We have isolated the cDNA of the 70-kDa peroxisomal membrane protein (PMP70) from rat and human liver cDNA libraries. The nucleotide sequence of the cDNA of PMP70 contains an open reading frame of 1977 bp which encodes an amino acid sequence of 659 residues. Possible two domains were identified by hydropathy analysis. One is a hydrophobic region, which presumably contains six transmembrane segments. The other is a hydrophilic domain, which shows striking similarity to the sequences of the ATP-binding cassette (ABC) transporter proteins, including bacterial periplasmic transport proteins, the human multidrug resistance P-glycoprotein (MDR1), cystic fibrosis transmembrane conductance regulator (CFTR), and the putative adrenoleukodystrophy gene product (ALDP). Based on its transmembrane structure and the homology to ABC proteins, PMP70 may be involved in ATP-dependent transport through peroxisomal membrane.