Animal models are important to evaluate new treatment modalities. In the present paper a new animal model is described, in which the effects of intraperitoneal (i.p.) administration of cytostatic drugs on cancers restricted to the peritoneal cavity can be studied. The tumor cell line used is a chemically induced carcinoma (CC531), sensitive in vitro to cisplatin (cDDP), carboplatin (CBDCA), 5-fluorouracil (5-FU), doxorubicin and mitoxantrone. Three to 5 weeks after i.p. inoculation of 2 x 10(6) CC531 cells, 80% of Wag/Rij rats develop small tumor nodules on peritoneal surfaces. Both tumor size and localization at this time are comparable to the human situation, especially to cases of minimal residual disease ovarian carcinoma. The model has been used to determine the usefulness of i.p. treatment in comparison to i.v. Changing the route of administration of cDDP from i.v. to i.p. increases tumor platinum concentrations and prolongs survival. The model offers the possibility to study drug pharmacokinetics and tumor drug penetration related to i.p. drug administration.