Do chemotherapeutic drugs have effects on the offspring of treated individuals? These authors treated male mice with clinically relevant doses of one of three widely used anticancer drugs and then measured the mutation rate at an expanded simple tandem repeat in the bone marrow and germline of their offspring using single-molecule PCR. They found a significant increase in mutations in both tissues and, intriguingly, in the maternal allele as well as the allele from the exposed father. It will be interesting to study the molecular basis of the effect and whether similar influences are seen in humans.