Protein phosphatase (PP2Calpha) is a member of the mammalian serine threonine-specific protein phosphatases family. We produced monoclonal antibodies against the recombinant PP2Calpha and evaluated the immunoreactivity of normal human tissues. The reactivity was strong in normal skin, the digestive tract, lung, kidney, breast, prostate, endocrine glands, and brain, while it was moderate in the ovary, testis, and liver. Epithelial cells revealed high levels of PP2Calpha expression, but stromal cells, including fibroblasts and endothelial cells, showed no or little PP2Calpha expression. Given the broad reactivity in endocrine and secreting epithelial cells, we propose that PP2Calpha expression might contribute to secretory cell function.