Alteration of T-cell-associated signal transduction molecules has recently been implicated in immune suppression in tumour-bearing hosts. Here we report the immunoregulatory effects of human lactoferrin (LF) on zeta-chain expression in peripheral blood T lymphocytes from cervical cancer patients and healthy donors. By quantitative flow cytometry analysis, we demonstrated that the mean zeta-chain expression was significantly higher in freshly-isolated T lymphocytes from healthy donors (69%), compared with the patients (38%). Following 3-day culture under standard conditions, zeta-chain expression in T lymphocytes from the patients increased significantly, whereas it dropped in the cells from healthy donors. Anti-CD3 MoAb as well as LF, significantly increased expression of zeta-chain in T cells both from patients and control subjects. The addition of LF to the anti-CD3 MoAb cell cultures resulted in an even higher stimulation of the zeta-chain expression. The results suggest that, in patients with cervical cancer, zeta-chain defects could be corrected by the therapeutic application of LF.