Antibody dependent lymphocyte (K cell) mediated lysis of tumor cells in vitro was used to assay for cell surface associated carcinoembryonic antigen (CEA) and two CEA-related normal tissue components, "normal glycoprotein" (NGP) and biliary glycoprotein I (BGP I). Three tumor cell lines were used as target cells. These were HT-29, colon carcinoma, T-24, urinary bladder transitional cell carcinoma and Mel-1, malignant melanoma. To induce lysis we used the IgG-fraction of specific rabbit and monkey anti-CEA sera and of specific rabbit anti-NGP and anti-BGP I sera, respectively. Purified human lymphocytes were used as effector cells. HT-29 was efficiently killed by low concentrations of rabbit anti-CEA and less efficiently by monkey anti-CEA. T-24 and Mel-1 were not lysed by anti-CEA, HT-29 and T-24 were lysed by low concentrations of anti-BGP I. In contrast only HT-29 was lysed by anti-NGP. Only a fraction of the tumor cells was killed by the different antisera although kinetic studies showed that the lytic reaction was complete well before the end of the eighteen hour incubation period used in the assay. Anti-CEA and anti-BGP I gave 30-40% corrected lysis of HT-29. With anti-NGP the corresponding figure was 10-20%.