The pharmacokinetics of doxorubicin in nude mice have been investigated following intravenous and intraperitoneal administration of single doses of 12 mg/kg. The areas under the concentration curves of doxorubicin in kidney, heart, and striated muscle following intraperitoneal administration were approximately half the areas following intravenous injection, whereas plasma and liver showed nearly identical concentrations after a distribution phase of 2 h. Only minor differences in pharmacokinetics were found between nude and normal mice.