Genomic-size RNA isolated from purified potato carlavirus M (PVM) was translated in both the reticulocyte and the wheat germ cell-free, messenger-dependent systems. The PVM RNA translated the same set of major products in both in vitro systems. The Mr values of the most prominent polypeptides observed consistently were 185,000 (P185), 147,000 (P147), 94,000 (P94), 87,000 (P87), 72,000 (P72), 67,000 (P67), 52,000 (P52), 46,000 (P46), 35,000 (P35) and 25,000 (P25). Relatively low amounts of a translation product of Mr 200,000 (P200) were often detectable in both systems. The P35 polypeptide displayed the same molecular weight and one-dimensional peptide map as the virus coat protein (CP), and was precipitated by antibodies raised against PVM and PVM CP. The kinetics of appearance of the in vitro synthesized polypeptides suggested that primary translation products of high molecular weight undergo post-translational proteolytic cleavage.