In the current study DNA-ploidy was determined in a group of 11 desmin-positive rhabdomyosarcomas and found to be aneuploid in all of them. In three cases, synchronous metastases could be studied as well. In two of them a hypotetraploid peak was observed not present in the primary tumor. In two other cases residual tumors obtained after chemotherapy appeared to have DNA-profiles similar to those observed in their primary tumors. These findings suggest either a selection of metastasizing clones or tumor progression. No apparent selection of clones responding to therapy could be established. For comparison, a group of other childhood sarcomas (four Ewing's sarcomas, two primitive neuroectodermal tumors, and two epithelioid sarcomas) was also studied. All except one of these cases appeared to have diploid or near-diploid stemlines. These results suggest that DNA-ploidy may be used as an additional criterion in the differential diagnosis of childhood sarcomas.