Several studies showed that thymic factors and prostaglandin synthesis inhibitors enhance in vitro lymphoproliferative response (LPR) to mitogens in cancer patients. In this study we investigated whether indomethacin and thymic extract (Thymex L), applied in combination, may in a synergistic pattern influence phytohemagglutinin-induced LPR in lung cancer patients. The results demonstrate that the use of the investigated agents enhances LPR to a similar level in hyporeactive patients before, as well as after, therapy. However, this drug combination exerts an additive effect on LPR, but only in patients who underwent cytoreductive radiation therapy, indicating the potential usefulness of this drug combination as an adjuvant treatment of these patients.