The combination of bolus doxorubicin and paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) as a 3-hour infusion is highly active in patients with metastatic breast cancer, but it has considerable cardiotoxicity. In this ongoing study, the potential effect of increasing the interval between administration of a short infusion of doxorubicin followed by a 3-hour infusion of paclitaxel was evaluated. Included were patients with metastatic breast cancer, who received doxorubicin 50 mg/m2 followed by paclitaxel 200 mg/m2 at intervals of 30 minutes, 4 hours, and 24 hours every 3 weeks. As of February 1997, 34 patients have been enrolled, two patients are too early to evaluate, and 13 are continuing treatment. The preliminary response rate is 69% (95% confidence interval, 50% to 84%), ranging from 60% to 80% within the three schedules. The main toxicities consisted of grade 3/4 neutropenia in 65% of all courses, with febrile neutropenia in 2%. Stomatitis and paresthesia were rare. To date, eight of 32 patients have developed abnormal left ventricular ejection fraction values and one patient has developed congestive heart failure. Our preliminary conclusions are that bolus doxorubicin followed by a 3-hour infusion of paclitaxel is highly active against metastatic breast cancer. The potential for cardiotoxicity with the regimen is reduced considerably if the maximum recommended cumulative dose of doxorubicin is reduced to 360 mg/m2 with a maximum single dose of 50 mg/m2.