Solute carrier family 21/O (SLC21/SLCO) is a group of organic anion transporters, which facilitate Na+-independent transport of organic anions and cations, including bile acids, steroid conjugates, and thyroid hormones. SLCO5A1/SLC21A15, also known as OATP5A1, has been detected at the transcriptional level in various human tissues such as those of the brain, skeletal muscle, kidney, and pancreas. Multiple transcript variants of the gene encoding OATP5A1 that are generated by alternative splicing have been registered. Substrates of the OATP5A1 transporter remain unknown.