Fanconi anemia (FA) is an autosomal recessive disease characterized by congenital anomalies, aplastic anemia, and chromosomal instability. A cDNA encoding the FA complementation group C (FACC) polypeptide was recently cloned [Strathdee, C. A., Gavish, H., Shannon, W. R. & Buchwald, M. (1992) Nature (London) 356, 763-767]. To further characterize this polypeptide, we generated a rabbit polyclonal antiserum against its carboxyl terminus. We used this antiserum to analyze the FACC polypeptide from normal or mutant (FA) lymphoblast cell lines. By immunoprecipitation, the wild-type FACC was a 60-kDa protein, consistent with its predicted molecular mass. FA group C cell lines expressed full-length FACC, truncated FACC, or no detectable FACC polypeptide. In addition, the antiserum specifically immunoprecipitated a 50-kDa and a 150-kDa FACC-related protein (FRP-50 and FRP-150). Unexpectedly, cell fractionation and immunofluorescence studies demonstrated that the FACC polypeptide localizes to the cytoplasm. In conclusion, we have generated an antiserum specific for the human FACC polypeptide. The antiserum should be useful for screening FA cells for mutant FACC polypeptides and for identifying and cloning FACC-related proteins.