Chemically induced sarcomas of inbred mice express antigens that are distinct and specific for each individual tumor. Chromosome assignment of tumor-specific antigens would help to elucidate the genetic basis of their diversity. Expression of the serologically defined Meth A sarcoma antigen is not suppressed in hybrid cells containing a complete foreign (Chinese hamster) genome. Chromosome and serologic analysis of microcell hybrids between Meth A sarcoma cells and Chinese hamster cells shows a clear correlation of Meth A antigen expression with the presence of the distal region of chromosome 12 (bands F1 and F2). Chromosome 16 may also be implicated. The significance of the close linkage of genes determining Meth A antigen expression with the immunoglobulin heavy chain gene cluster (on chromosome 12) and the lambda light chain genes (on chromosome 16) is discussed.