Two independent studies have compared killed C. parvum (CP) vaccine with viable BCG (Pasteur) and BCG (Glaxo) vaccines, respectively, for potentiation of antitumor immunity when injected with irradiated tumor cells into B6D2F1 and CBA-T6 T6 mice. Both studies concurred that, for a given number of irradiated tumor cells, larger amounts (dry weight equivalent) of BCG than CP were required to produce similar degrees of tumor immunity. Evidence also showed that stronger and more protracted immunity was mediated by CP than by BCG.