We determined pre- and post-photodynamic therapy (PDT) serum levels of soluble interleukin-2 receptor (SIL-2R) and interleukin-2 (IL-2), as well as activity of natural killer (NK) cells, among 24 patients with either persistent or recurrent nasopharyngeal carcinoma (NPC), using a double-antibody sandwich technique, tritiated thymidine-deoxyribonucleoside incorporation, and iodine 125-uridine-deoxyribonucleoside release techniques, respectively. The results showed that the post-PDT serum level of SIL-2R had significantly declined (p < .0005), while that of IL-2 and the NK cell activity had significantly increased (p < .0005), compared with pre-PDT values, suggesting an immunoenhancing effect of PDT on NPC patients.