Over the last four years a guinea pig model of active-specific immunotherapy (ASI) with a syngeneic tumor cell:bacillus calmette-Guerin (BCG) vaccine was translated into a prospectively randomized, controlled clinical trial in patients with colorectal cancer. Primary tumors from patients undergoing standard surgical resection were dissociated enzymatically and cryopreserved by techniques that maintain cell viability. Patients with transmural extension of tumor or nodal metastases were randomized into groups treated by resection alone (control) or resection plus ASI. With a mean follow-up of 28 months (range, 14-24), only 3 of 20 treatment patients had recurrences and none have died, whereas 9 of 20 control patients had recurrences and 4 died. These differences are statistically significant and are sufficiently encouraging to warrant expansion of these studies into other research centers.