Intracellular signal transduction pathways play a crucial role in a variety of cellular processes, such as differentiation, proliferation, or apoptosis, and the reversible phosphorylation of their components is a major regulatory mechanism to control their activities. While much has been learned about the contribution of kinases, the involvement of phosphatases in these events is less clear and has only recently received more investigative attention. The availability of various natural product inhibitors of phosphatases has helped enormously to gain insight into the role that these enzymes exert in various signal transduction processes. This review will focus on serine/threonine protein phosphatase type 2A (PP2A) and will present findings pertaining to its involvement in cellular signal transduction pathways. Since the majority of these studies were done with the use of phosphatase inhibitory compounds, some pros and cons of their application will be presented.