A comparison of the physical properties and immunoreactivity of ectopic hCGB from cultured cervical cancer cells and standard hCGB was performed. The heterogeneity of the preparations was examined by ion-exchange chromatography, and the molecular size by analytical gel filtration. Two distinct forms of ectopic hCGB were identified. One form was indistinguishable from standard hCGB, while the other, although larger, lacked the characteristic COOH-terminal peptide (CTP). This was shown by the failure of antisera specific for determinants on the CTP to recognize this molecule, and by the apparent absence of the 0-1 inked oligosaccharides and thermolysin cleavage site normally found in this region.