The novel organic cation transporter 1 (OCTN1) is a multispecific, bidirectional and pH-dependent organic cation transporter with low carnitine transport activity. It is a transporter of the physiological substance ergothioneine and mediates the transport of a variety of organic cations such as tetraethylammonium, pyrilamine and quinidine. This study identifies genetic variations of the SLC22A4 gene in two distinct ethnic groups of the Singaporean population (n=192) by DNA sequencing. Twenty four genetic variants of SLC22A4, including 14 found to be novel. 16 in the coding exons (10 nonsynonymous and 6 synonymous variations) and 8 in the introns. Among the novel nonsynonymous variations, Arg63His, Arg83Pro, Met344Lys and Ile500Asn were predicted to be functionally significant. These data should provide fundamental and useful information for pharmacogenetic studies on drugs that are substrates of OCTN1 in Asians.