A human choline kinase cDNA was cloned by complementation of the yeast choline kinase mutation, cki, from a human glioblastoma cDNA expression library. The deduced sequence of the human enzyme comprised 456 amino acids with a calculated relative molecular mass of 52,065. The human enzyme resembled the rat liver enzyme over the entire sequence. It also resembled the yeast enzyme in the carboxy-terminal region, but not much in the amino-terminal region.