Cell-mediated immunity versus tumor antigens (cytosols) of the same histotype and site was evaluated by means of the leukocyte adherence inhibition (LAI) test in 44 colorectal adenocarcinoma and 17 lung squamous-cell carcinoma patients 3-10 years after surgical resection. LAI-positivity was observed in 17/44 (38.6%) and 13/17 (76.5%) patients, respectively, together with serum blocking factors in 7/17 (41.2%) compared to 0/13. These results indicate that a high percentage of long survivors retain an immunologic memory of the tumor antigen to which they have been exposed. The prognostic significance of serum blocking factors is less clear.