We performed a phase II, Southwest Oncology Group (SWOG) clinical trial of recombinant human interleukin-4 (rhuIL-4) in patients with previously treated non-Hodgkin's lymphoma (NHL). We studied 18 eligible patients with low-grade and 21 patients with intermediate- or high-grade NHL. All patients had received prior chemotherapy. A protocol amendment after the first four patients reduced the frequency of s.c. rhuIL-4 administration from daily to 3 times per week at 3 microg/kg and limited the number of prior chemotherapy regimens allowed. We documented no complete or partial responses in the low-grade NHL group [0%; 95% confidence interval (CI) 0-19%]. One patient in the intermediate/high-grade NHL group developed a partial response lasting longer than 15 months (5%; 95% CI 0-24%). Median survivals for the low- and intermediate/high-grade NHL groups were 15 and 13 months, respectively. Common toxicities included: arhralgia/myalgia, fatigue/malaise/lethargy, fever, headache, nausea and rigors/chills. Cardiac toxicity, gastrointestinal ulceration and nasal congestion due to rhuIL-4 were not prominent toxicities in our patients. Our previously treated NHL patients tolerated s.c. rhuIL-4 at a dose of 3 microg/kg given 3 times per week, but objective response rarely occurred. Further evaluation of rhuIL-4 in these patient populations does not appear warranted.