Multidrug-resistant (MDR+) cancer cells have the ability to grow in the presence of cytotoxic concentrations of antineoplastic drugs as a result of possessing the transmembrane drug efflux pump p-glycoprotein. The MDR+ colonic cancer cell line LoVoDx (derived from the drug-sensitive line LoVo) was tested for sensitivity to lymphokine-activated killer (LAK) cell-mediated toxicity. LAK cells were cultured from patients with colonic cancer and from matched controls with benign disorders. LAK cells from patients with cancer were as effective as those from controls in mediating cytotoxicity. The MDR+ cell line was significantly more sensitive to LAK cell-mediated cell killing than its parental drug-sensitive line LoVo (P < 0.05). These results indicate a possible role for adoptive immunotherapy in MDR+ tumours expressing p-glycoprotein.