The in vivo mechanism of action of alemtuzumab (anti-CD52; Campath-1H) remains unclear. With rituximab, FCGR3A and FCGR2A high-affinity polymorphisms have been associated with clinical response in lymphoma but not in CLL, suggesting potential divergent mechanisms of action between these 2 diseases. Herein, we examined FCGR3A (V/V, n = 4; V/F, n = 10; F/F, n = 19) and FCGR2A (A/A, n = 5; H/A, n = 22; H/H, n = 6) polymorphisms in 36 patients with relapsed CLL who were treated with thrice-weekly alemtuzumab for 12 weeks to assess the potential influence these high-affinity FcgammaR receptor polymorphisms had on response to alemtuzumab. Response to alemtuzumab was similar regardless of FCGR3A polymorphism (V/V, 25%; V/F, 40%; F/F, 32%) or FCGR2A polymorphism (A/A, 40%; H/A, 32%; H/H, 33%). These findings indicate that FCGR3A and FCGR2A polymorphisms may not predict response to alemtuzumab in CLL. Future studies examining larger cohorts of alemtuzumab-treated patients with CLL will be required to definitively determine the predictive value of specific FCGR polymorphisms to treatment response.