Valosin, a novel 25-amino-acid peptide isolated recently from pig intestine, has several effects on the digestive system of dogs. We report here that the valosin-specific complementary DNA clone from pigs codes for a polypeptide unlike most precursors of biologically active peptides. The predicted protein lacks a characteristic amino-terminal hydrophobic signal sequence and contains no processing signals of the type acted upon by endopeptidases to generate other active peptides from precursors. Antibodies to synthetic valosin have been used to show that nearly all valosin immunoreactivity is in the cytoplasm and that the protein detected (valosin-containing protein, VCP), although smaller than the predicted product of the cDNA sequence, is much larger than valosin. Valosin-specific messenger RNA is found in extracts from many pig tissues, which contrasts with the restricted occurrence expected of a biologically active peptide. We conclude that valosin is an artefact of the purification procedure and does not occur in vivo.