The role of glutamine (GLN) in the generation of lymphokine-activated killer (LAK) cell activity was investigated. LAK cells were derived from healthy donors and peripheral blood mononuclear cells (PBMC) were obtained using either unseparated PMBC or DR(-) CD3(-) CD16(+) CD56(+) enriched cells. PBMC were cultured for 6 or 10 days in medium supplemented with recombinant interleukin-2 (rlL-2; 100 U/ml) in the presence of different concentrations of GLN. K562 (natural killer-NK-sensitive targets), 1301 and U-937 (NK-resistant targets) cells were used as targets in the cytotoxic assays. Furthermore, the limiting dilution (LD) culture system was applied as an alternative to the bulk cell culture system. It was found that GLN affects the lytic potential of cultured cells while the frequency of responding cells did not significantly differ between the compared cell cultures performed in the presence of different amounts of GLN. Data on cell proliferation with IL-2 stimulation showed significant differences in cultures performed in the presence or absence of GLN. The results of present investigation suggest a supportive role of GLN in the generation of LAK cells. GLN deficit affects LAK cell killing activity by limiting the number of generated effector cells while acquisition of broad-range killing capacity was not affected.