We have tested by the computerized tube leukocyte adherence inhibition (LAI) assay, 319, 100 and 342 patients and controls for the presence of antitumor immunity to colorectal, breast and lung cancers. The assay was standardized and its sensitivity increased by using, as a challenging antigen, spent medium of human carcinoma cell lines and by the addition of prostaglandin E2 (PGE2). By large, the sensitivity of the assay (after the addition of PGE2) was inversely related to tumor burden, namely, it was 82.7, 78.9, and 88.6% as compared to 57.1, 33.3, and 29.6% for the early and late stages of colorectal, breast and lung cancers, respectively. Calculating the frequency of disease in the population studied and in comparison with known frequencies of the same in the general population, the positive and negative predicting values (PVpos, PVneg) were obtained. Our results demonstrate that the LAI assay cannot be applied for mass screening since its low PVpos would impair its effectiveness. However, its application to a population at high risk for developing a particular malignancy or as a second-line modality to more conventional screening methods would increase its cost-effectiveness and favor its applicability.