OUTLINE: This is a dose escalation study of interleukin-12. Patients receive rituximab IV on days 1, 8, 15, and 22. The first cohort of patients receives interleukin-12 SC twice weekly beginning on day 29. Subsequent cohorts receive interleukin-12 SC twice weekly beginning on day 16. Patients with stable or responding disease may continue treatment with interleukin-12 twice weekly for up to 24 weeks or until disease progression. Cohorts of 6-9 patients receive escalating doses of interleukin-12 until the optimal immunological dose is determined. The optimal immunological dose is defined as the dose preceding that at which 2 of 6 or 2 of 9 patients experience dose limiting toxicities or the dose at which there is a maximal increase in gamma interferon, inducible protein-10 (IP-10) and immune cell infiltration into the lymphoma (whichever dose is lower). Following initial dose escalation, 2 additional cohorts of 6 patients receive a fixed dose of interleukin-12 SC twice weekly beginning on day 2. Patients are followed every 3 months for the first year, and then every 6 months for the next 4 years or until disease progression.