The presence of interleukin (IL)-6 in peritoneal carcinomatous fluid (PCF) and its effect on immune cells composition in PCF in patients with advanced ovarian carcinoma was studied. In 21 out of 30 ovarian carcinoma patients, PCF IL-6 levels were found to exceed those seen in PCFs of patients with gastrointestinal cancer. IL-6 activity was higher in serous/mucinous than in endometrioid and undifferentiated ovarian carcinoma PCF (P = 0.05). Ovarian carcinoma PCF IL-6 activities were correlated with serum C-reactive protein levels (r = 0.65, P = 0.0000, n = 25). Ovarian carcinoma PCF leucocyte profile differed from that in blood with respect to: (i) lower percentage of NK and CD8+ and (ii) higher percentage of B and CD45RO+, CD14+ and HLA-DR+ cells. The proportions of CD45RO+ in blood were correlated with IL-6 levels in PCF. Corresponding to PCF ovarian carcinoma tumours were stained for the presence of Ki-67 antigen and p53. The highest proportions of Ki-67+ cells and cells showing accumulation of p53 were seen in undifferentiated tumours. A low grade of p53 staining was seen in tumours associated with high IL-6 levels in PCF. It was evident that IL-6 production (i) depended on the histiotype of the tumour, (ii) influenced the local immune system in favour of accumulation of B, and T memory cells, and (iii) was higher in patients lacking p53 accumulation.