Since both doxorubicin and paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) have substantial antitumor activity in advanced breast cancer, the combination of these two agents was a logical extension of the clinical development of paclitaxel. Early attempts used long infusions of both drugs, limiting the dose of both agents because of limiting gastrointestinal and myelosuppressive toxicity. Bolus doxorubicin combined with 3-hour infusion paclitaxel was reported to have dramatic antitumor activity, but clinically relevant cardiac toxicity in up to 20% of patients in two recent reports. In our current study the same schedules and doses of administration were used, limiting the total doxorubicin dose of 360 mg/m2. In-depth monitoring of cardiac function with noninvasive tests and endomyocardial biopsy were performed. Preliminary results suggest that, at these doses and schedule, the two-drug combination is safe, without unexpected toxicity. Limiting doxorubicin dose to 360 mg/m2 limits cardiac toxicity to levels expected from single-agent doxorubicin at similar cumulative doses.