The biological activity of recombinant Interleukin-2 (rIL-2) administered intraperitoneally (ip) has not been determined and may differ significantly from the maximum tolerated dose (MTD). In this trial, the pharmacokinetics, toxicity, and biologic activity of a single ip dose were studied initially followed a week later by a 5-day ip rIL-2 given for 2 weeks every 28 days. Planned dose escalation was from 2 x 10(3) to 2 x 10(7) U given in 2 liters of D5W. Drug was obtained from the NCI and was administered through an ip port. Four patients received 1 U/ml and four patients received 10 U/ml. Preliminary data demonstrate an increase in the peritoneal fluid mononuclear cell count. Mononuclear cell phenotyping tested in the first eight patients showed a modest increase in Leu 2a+, Leu 15- cells, corresponding to CTL. A similar increase in Leu 19+ cells was also demonstrated (NK cells). Soluble IL-2 receptor was elevated in peritoneal fluid. Cytotoxicity against K562 and Daudi cell lines was not observed at the first two dose levels. Toxicity of treatment was minimal and related to abdominal distention. No objective responses were seen but in one patient we documented a reduction in serum CA-125 levels. The observed biologic response and lack of toxicity is promising and justifies further exploration of this immune-modulating approach.