CV2 antibodies (CV2-ab) associate with paraneoplastic neurological syndromes (PNS) and small-cell lung cancer. This study was designed to assess the sensitivity of two widely used anti-CV2 commercial kits. Fifty three sera with CV2-ab identified by immunohistochemistry on paraformaldehyde-perfused rat brain were tested with two commercial immunoblot kits (Euroimmun AG, and Ravo Diagnostika) and 4 (7.5%) of them were negative with the commercial kits. The 4 samples were positive by immunofluorescence on HEK293 cells transfected with CRMP5 and immunoblot of these cells lysate. A few CV2-ab-positive sera may be missed by commercial immunoblots. Negative samples from patients with high suspicion for PNS should be tested by alternative methods.