The present study was designed to investigate the in vivo effect of local application of lymphokine-activated killer (LAK) cells on the growth of tumours implanted under the renal capsule in nude mice, and especially to test whether large granular lymphocytes (LGL), regarded as natural killer (NK) cells, are the main precursor of LAK cells in vivo. Our results showed that the local application of LAK cells inhibited the growth of tumours in the head and neck region. The growth of tumours implanted under the renal capsule was inhibited by local application of 1 x 10(7) recombinant interleukin-2 (rIL-2) activated non-adherent lymphocytes, but the inhibitory effect was almost the same as produced by 3 x 10(6) rIL-2-activated LGL application. The findings indicate that the rIL-2-activated LGL are the main effectors in inhibiting tumour growth. In addition, rIL-2-activated non-adherent lymphocytes as well as LGL significantly prolonged the number of days of 50% survival and mean survival time of nude mice, in which HLaC78 cells, from a laryngeal tumour cell line, were injected into the subrenal capsule space with effector cells at various effector: target (E:T) ratios. The results indicate that the application of LAK cells may be useful in the treatment of patients with head and neck tumours.