We have cloned the full-length cDNA for the human ATP binding cassette transporter 1 (hABC1). The 6603-bp open reading frame encodes a polypeptide of 2201 amino acids resulting in a deduced molecular weight of 220 kDa. The hABC1 cDNA is highly homologous (62%) to the human rim ABC transporter (ABCR). hABC1 is expressed in a variety of human tissues with highest expression levels found in placenta, liver, lung, adrenal glands, and fetal tissues. We demonstrate that the hABC1 expression is induced during differentiation of human monocytes into macrophagesin vitro.In macrophages, both the hABC1 mRNA and protein expression are upregulated in the presence of acetylated low-density lipoprotein (AcLDL). The AcLDL-induced increase in hABC1 expression is reversed by cholesterol depletion mediated by the addition of high-density lipoprotein (HDL₃). Our data, demonstrating sterol-dependent regulation of hABC1 in human monocytes/macrophages, suggest a novel role for this transporter molecule in membrane lipid transport.