Interleukin-6 (IL-6) and tumour necrosis factor-alpha (TNF-alpha) are important multifunctional cytokines involved in tumour growth and metastasis. In this study, we have measured serial levels of serum IL-6 and TNF-alpha in prostate cancer patients. A total of 80 patients with carcinoma of the prostate and 38 controls were studied. Three patient groups, with small bulk localised, large volume localised and metastatic prostate cancer, were assessed. Serum IL-6 and TNF-alpha levels were measured and correlated with clinicopathological variables and patient survival. Serial changes in these cytokines were also assessed and related to disease progression in 40 patients with recurrent prostate cancer. Serum IL-6 levels in patients with metastatic disease (9.3+/-7.8 pg x ml(-1)) were higher than those in patients with localised disease (1.3+/-0.8 pg x ml(-1), P<0.001). Significantly elevated levels of TNF-alpha were found in metastatic disease (6.3+/-3.6 pg x ml(-1)) compared with localised disease (1.1+/-0.5 pg x ml(-1), P<0.001). The levels of both cytokines were directly correlated with the extent of the disease. Serial analysis in 40 patients with recurrent tumours showed that both cytokines became elevated at the point of prostate-specific antigen progression. In conclusion, these results suggest that IL-6 and TNF-alpha correlate with the extent of disease in patients with prostate cancer and may be monitored in conjunction with other disease markers.