Iodinated cell surface polypeptides of human-mouse somatic cell hybrids were analyzed by one-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis and high resolution two-dimensional gel electrophoresis in an effort to identify human gene products. Expression of two cell surface polypeptides was positively correlated with retention of specific human chromosomes: a polypeptide of molecular weight 250,000 and isoelectric point 8.3 with the human 5, and a polypeptide of molecular weight 250,000 and isoelectric point 7.0 with the human 2.