In this report, the molecular weight and antigenicity of the proteins of a porcine enteric calicivirus (PEC) were characterized. The PEC virions were purified from intestinal contents of infected pigs and from infected cell culture lysates. The average buoyant density of the purified virus was 1.37 gm/cm3 in cesium chloride. One major structural protein with a molecular weight of approximately 58 k was found in the gut and cell culture-passaged PEC using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Using immunoblotting techniques only one immunoreactive protein (58 k) ws identified. The PEC and a prototype calicivirus, feline calicivirus (FCV) were propagated in pig kidney and feline kidney (Crandell) cell lines, respectively and intrinsically labeled using [35S]methionine at various times post-inoculation (PI). SDS-PAGE of the radiolabeled proteins indicated the presence of the major structural protein (58 k) and one probable nonstructural protein (28 k) synthesized in the PEC-infected cell lysates by 12 h PI. Other minor protein bands were also evident by 24 h PI (32 k and 82 k). Only the 58 k major protein was detected by radioimmunoprecipitation (RIP) analysis using hyperimmune anti-PEC serum. SDS-PAGE and RIP analysis of FCV-infected cell lysates using hyperimmune anti-FCV serum identified a single major protein of approximately 64 k. No antigenic relationship between PEC and FCV proteins was detected by RIP analysis. The single major structural protein of PEC, the morphological appearance and size of the virus, and its average density of 1.37 gm/cm3 in cesium chloride are consistent with properties of other members of the family Caliciviridae.