In the tumor-dormant state intended for further study, small numbers of lethal L5178Y lymphoma cells persist in the peritoneal cavity of clinically normal DBA/2 mice for many weeks before growing out to produce an ascitic tumor. We have identified host cells involved in the establishment, maintenance, and termination of the tumor-dormant state. We intend here to modulate the growth-restraint mechanisms that maintain the tumor cells in a dormant state and to manipulate the dormant tumor cell population so as to either prolong or terminate the tumor-dormant state. We will further characterize the tumor cells isolated at various stages of tumor-dormant state and evaluate the effects of pregnancy and stress on the tumor-dormant state. (MI)