Transgenic female mice carrying the V-Ha-ras transgene linked to the MMTV promoter, which developed mammary carcinomas, were treated with selected cancer chemotherapy drugs. Agents were administered i.p. on a daily x 9 schedule when mice developed tumors that were 50-100 mg in size. Drugs which are clinically effective against breast cancer were quite efficacious in the transgenic model at their maximum tolerated dose. Doxorubicin produced excellent responses in tumor-bearing transgenic mice, with several mammary carcinomas undergoing tumor shrinkage. Two anthrapyrazoles, DuP 937 and DuP 941, novel anticancer drugs with phase 2 activity against breast cancer, were as effective as doxorubicin in the oncomice. Mitoxantrone, a synthetic agent with some properties similar to the anthracyclines, also had antitumor activity, but not as pronounced as obtained with doxorubicin or the anthrapyrazoles. Cisplatin, a drug with limited use in human breast cancer, only caused modest antitumor responses. A computerized data analysis method based on the area under the tumor growth curve was developed to better quantitate the data and provide statistical information. This quantitative analysis confirmed the high statistical significance of the activity of doxorubicin or the anthrapyrazoles in the ras transgenic model, and defined an excellent dose response relationship for each drug tested. Our results suggest that the ras transgenic model may be useful for identifying drugs that have efficacy for breast cancer in women.