Gel filtration and radioimmunological studies were used to demonstrate that BeWo malignant trophoblastic cells, subcultured for more than 12 yr as roller tube colonies using dissection by scalpel, retained the ability to secrete large quantities of intact hCG. By contrast, BeWo cells that had been subcultured weekly for 12 hr using proteolytic enzyme dispersion lost their ability to secrete intact hCG. Rather, a large form of hCG-alpha was the major secretory product, along with lesser amounts of heterogeneous low molecular weight forms of hCG-beta. The gradual loss of hormone secretory ability and fidelity of hormone product by cells in continuous culture is a well known phenomenon. Our results suggest that the habitual use of trypsin-EDTA to subculture cells may accelerate this process.