A liver-speciˆc transporter organic anion transporting polypeptide 1B1 (OATP1B1, also known as OATP-C) is encoded by SLCO1B1 and mediates uptake of various endogenous and exogenous compounds from blood into hepatocytes. In this study, 15 SLCO1B1 exons (including non-coding exon 1) and their‰ anking introns were comprehensively screened for genetic variations in 177 Japanese subjects. Sixty-two genetic variations, including 28 novel ones, were found: 7 in the 5′-‰ anking region, 1 in the 5′-untranslated region (UTR), 13 in the coding exons (9 nonsynonymous and 4 synonymous variations), 5 in the 3′-UTR, and 36 in the introns. Five novel nonsynonymous variations, 311T> A (Met104Lys), 509T> C (Met170Thr), 601A> G (Lys201Glu), 1553C> T (Ser518Leu), and 1738C> T (Arg580Stop), were found as heterozygotes. The allele frequencies were 0.008 for 1738C> T (Arg580Stop) and 0.003 for the four other variations. Arg580Stop having a stop codon at codon 580 results in loss of half of transmembrane domain (TMD) 11, TMD12, and a cytoplasmic tail, which might aŠect transport activity. In addition, novel variations, IVS12-1G> T at the splice acceptor site and-3A> C in the Kozak motif, were detected at 0.003 and 0.014 frequencies, respectively. Haplotype analysis using-11187G> A,-3A> C, IVS12-1G> T and 9 nonsynonymous variations revealed that the haplotype frequencies for* 1b,* 5,* 15, and* 17 were 0.469, 0.000 (not detected), 0.037, and 0.133, respectively. These data would provide fundamental and useful information for pharmacogenetic studies on OATP1B1-transported drugs in Japanese.