Protein phosphatase activities in extracts of the yeast Saccharomyces cerevisiae showed remarkable similarities to the mammalian type 1, type 2A and type 2C enzymes. Similarities included their substrate specificities, including selectivity for the alpha-and beta-subunits of muscle phosphorylase kinase, sensitivity to okadaic acid and to mammalian inhibitor 1 and inhibitor 2, and requirement for divalent cations. The results suggest that the function and regulation of these enzymes has been highly conserved during evolution and indicate that the improved procedure for identifying and quantitating protein phosphatases [(1989) FEBS Lett. 250,000,000] may be applicable to all eukaryotic cells.