The cytotoxic activity of lymphokine-activated killer (LAK) cells against enriched cultures of oligodendrocytes (OL) was investigated in multiple sclerosis (MS) and controls. Human LAK cells, derived from macrophage-depleted peripheral blood mononuclear cells (PBMC) and incubated with recombinant human interleukin-2 (IL-2) (20-80 U/ml), mediated high levels of cytotoxicity against Raji cells but low levels of cytotoxicity against primary cultures of bovine OL. Cytotoxicity was not enhanced by incubation with a high level of IL-2 (500 U/ml). No statistically significant differences in LAK cell activity against bovine OL were observed among the study groups. Enriched adherent LAK (A-LAK) cells mediated greater levels of cytotoxicity against both bovine OL and tumor cell lines than unfractionated LAK cells. Flow cytometric analysis indicated that A-LAK effector cells were CD4-, CD8+, and CD16+. Furthermore, A-LAK cells mediated lysis of OL derived from several different animal species. Our results suggest that LAK and A-LAK cells can mediate cytolysis of OL in culture similar to that observed with a number of different tumor cell lines. However, no significant difference in cytolysis was identified between MS and control groups in this study.