Nine patients with metastatic renal cell carcinoma were entered into a pilot protocol including a 4-week regimen utilizing human recombinant interleukin-2 (IL-2) and in vitro lymphokine-activated killer (LAK) cells. The regimen included 2 weeks (4 days of treatment and 3 days of rest/week) of continuous-infusion (c.i.) IL-2 at 3 x 10(6) U/m2/day, followed by two leukaphereses. LAK cells were cultured in vitro for 48 to 72 h and administered as a single infusion, followed by 9 days of bolus i.v. injections of 10(6) U IL-2/m2/dose, given every 8 hours (t.i.d.). The average (+/- SD) number of LAK cells infused per patient was 7.2 x 10(10) (+/- 3.5 x 10(10)). One patient showed > 50% shrinkage of tumor (lung + renal bed recurrence). Toxicity was similar to that encountered in other studies using similar IL-2 doses and LAK cells and consisted of fever, hypotension, fluid retention, and reversible renal insufficiency. These results indicate that the 2 weeks of IL-2 c.i. provided conditions enabling the harvest of large quantities of mononuclear cells from the peripheral blood of patients; this could be useful for future trials requiring the use of in vitro activated lymphocytes. Nevertheless, these pilot data suggest that this regimen of prolonged t.i.d. IL-2 administration after the LAK infusion does not seem to generate any improvement in antitumor effects from those obtained using other LAK + IL-2 regimens.