A single injection of antitumor anthracycline antibiotic in a maximum tolerated dose decreased mating capacity in male rats (doxorubicin, farmorubicin) and decreased the efficiency of mating (farmorubicin). In female rats mating capacity did not decrease, but some of them became sterile. The majority of toxic effects were reversible. The incidence of embryonal death before implantation was increased in intact females mated with males treated with farmorubicin. In females treated with anthracycline antibiotics high incidence of pre- and postimplantation embryonal deaths was noted.