The membrane protein CD36 has been implicated in platelet and monocyte signal transduction events and is known to be tightly associated with cytosolic protein tyrosine kinases. CD36 contains an extremely small cytoplasmic domain(s) and the mechanism by which CD36 interacts with cytosolic kinases is unknown. In the present study, CD36 (M_r88,000) has been detected on the surface of platelets as a conformational isoform or complex of apparentM_r113,000. In intact platelets crosslinked with bis(sulfosuccinimidyl)suberate, approximately 50% of cell surface CD36 existed as the 113-kDa form. When detergent extracts of platelets were crosslinked, the amount of CD36 in the 113-kDa form was found to be dependent on the detergent used. The 113-kDa form of CD36 was 10-fold more prevalent in Triton X-100 extracts than in extracts made with the zwitterionic detergent 3-[(3-cholamidopropyl)di- methylammonio]propanesulfonate (CHAPS). Addition of Triton X-100 to CHAPS platelet extracts resulted in recovery of the 113-kDa form of CD36. These studies suggest that CD36 exists on the surface of platelets as a heterodimeric complex of CD36 and another protein(s) or exists in two different conformational states which, when covalently crosslinked, exhibit an apparentM_rof 113,000. Further characterization of the 113-kDa form of CD36 may help define CD36–kinase interactions.