This prospective, open-label, pilot phase 2 study examined the clinical and immunologic effects of oregovomab (OvaRex) in heavily pretreated patients with recurrent ovarian cancer (OC). Thirteen women were administered intravenous oregovomab (2 mg) at weeks 0, 2, 4, 8, and 12, followed by quarterly doses for up to 2 years or disease progression. Concomitant chemotherapy was not permitted. Eligibility criteria included recurrence after one or more platinum-based chemotherapy regimens, CA125 >35 U/mL, evaluable or measurable disease. Tumor burden was evaluated by physical or radiologic methods pretreatment, weeks 12, 24, and every 24 weeks thereafter. Immune responses, including antibodies and T cells to oregovomab and CA125, were demonstrated in over half the patients. Stabilization of disease and survival >2 years was observed in 3 of 13 patients and coincided with robust immune responses. Shrinkage of marker lesions was not observed; however, four patients showed decreases in CA125 levels. Treatment was well tolerated without serious adverse events or discontinuations due to therapy. This pilot study supports immunologic activity and safety of oregovomab in recurrent OC. Further study of this agent in the consolidation and adjuvant setting is ongoing to establish its clinical utility.