NK activity of human peripheral blood lymphocytes (PBL) for cells of the human myeloid line K562, and antibody-dependent cellular cytotoxicity (ADCC) of PBL for cells of human lung adenocarcinoma line PC-9 were determined by the human tumor clonogenic assay (HTCA). Incubation of K562 cells or anti-PC-9 serum treated PC-9 cells with PBL before plating inhibited the formation of colonies of these tumor cells. The percent inhibition of tumor cell colony formation was dependent on the effector/target ratio, the incubation time before plating and, in the case of PC-9 cells, on the dilution of anti-PC-9 serum. PBL activated with human T-cell growth factor (TCGF), lymphokine-activated killer (LAK) cells, significantly augmented the inhibition of colony formation of K562 cells, compared to the control lymphocytes. The increase in colony inhibition was dependent on the concentration of TCGF and the time of incubation of PBL with TCGF. The HTCA determining the colony inhibition of K562 cells incubated with LAK or PBL correlated with the 51Cr-release assay (p less than 0.001). The HTCA determining the colony inhibition of anti-PC-9 serum-treated PC-9 cells incubated with PBL also correlated with the 51Cr-release assay (p less than 0.001). We found that the NK activity and ADCC of lymphocytes on K562 and PC9 tumor lines could be detected with HTCA.