Complementary DNA encoding a catalytic subunit of protein phosphatase 1, termed PP1 gamma, was isolated from a human teratocarcinoma library. The sequence suggests that alternative splicing produces two forms of PP1 gamma, designated PP1 gamma 1 and PP1 gamma 2, which differ in their C-termini. The gene for human PP1 gamma (PPP1CC) was localized to chromosome 12 by analysis of somatic cell hybrid DNA and mapped to bands q24.1-q24.2 by in situ hybridisation. These data show that although PP1 gamma 1 and PP1 gamma 2 are 94% and 93% identical to PP1 alpha respectively, the PP1 gamma gene is not closely linked to the PP1 alpha gene, which has been mapped to chromosome 11.