Here we describe the association of the synaptosomal plasma membrane Ca 2؉ -ATPase (PMCA) from pig cerebellum with cholesterol/sphingomyelin-rich membrane domains (rafts). The PMCA4 was localized exclusively in rafts prepared by floatation in Nycodenz density gradients of ice-cold Brij 96 extracts. This was corroborated by its colocalization with the raft markers cholesterol, ganglioside GM1, and PrP C . The remaining PMCA isoforms were found in the detergent-soluble fractions, with the majority of the membrane proteins. Activity assays confirmed the bimodal distribution of the PMCA isoforms in the density gradient, with a lower activity for PMCA4 and greater stimulation by calmodulin than for the other isoforms. By providing an ordered membrane microenvironment, lipid rafts may contribute to the interaction of PMCA4 with proteins involved in Ca 2؉ signaling at discrete functional positions on the synaptic nerve terminals.