The toxicity of Na-2,3-dimercaptopropane-1-sulfonate (DMPS) was investigated in rats. The lethality after large i.p. doses is diminished by a factor of approx. 6 if a single dose is divided into several doses on consecutive days. Chronic treatment with 600 mumol DMPS/kg and day p.o. did bring about adverse effects except a reduction in Cu-concentration in some organs, especially in the kidneys, immediately after DMPS-treatment, which was normalized within 1 week. The offspring of DMPS treated female rats showed no abnormalities.