OBJECTIVE Farletuzumab is a humanized monoclonal antibody to folate receptor-α, which is over-expressed in most epithelial ovarian cancers but largely absent on normal tissue. We evaluated clinical activity of farletuzumab, alone and combined with chemotherapy, in women with first-relapse, platinum-sensitive ovarian, fallopian tube and primary peritoneal cancers. METHODS Fifty-four eligible subjects received open-label farletuzumab weekly, single agent or combined with carboplatin (AUC5-6) and taxane (paclitaxel 175 mg/m(2) or docetaxel 75 mg/m(2)), every 21 days for 6 cycles, followed by farletuzumab maintenance until progression. Twenty-eight subjects with asymptomatic CA125 relapse received single-agent farletuzumab and could receive platinum/taxane chemotherapy plus farletuzumab after single-agent progression. Twenty-six subjects with symptomatic relapse entered the combination arm directly; 21 subjects entered after single agent. Primary endpoints included normalized CA125 and Overall Response Rate (ORR). Duration of each subject's second progression-free interval (PFI2) was compared with her own first response interval (PFI1). RESULTS Farletuzumab was well-tolerated as single agent, without additive toxicity when administered with chemotherapy. Of 47 subjects who received farletuzumab with chemotherapy, 38 (80.9%) normalized CA125. In 9/42 (21%) evaluable subjects, PFI2 was≥PFI1, better than the historical rate (3%). There was a high response rate among subjects with PFI1 <12 months (75%), comparable to that in subjects with PFI1 ≥12 months (84%). Complete or partial ORR was 75% with combination therapy. CONCLUSIONS Based on this study, farletuzumab with carboplatin and taxane may enhance the response rate and duration of response in platinum-sensitive ovarian cancer patients with first relapse after remission of 6-18 months.