Almost all the adjuvant chemotherapy regimens that have been established as effective in prolonging the survival of patients with early breast cancer have been administered for 1 to 2 years. If equally effective, shorter courses of therapy would result in less overall toxicity and allow early introduction of non-cross-resistant regimens. The efficacy of 2 regimens differing only in duration was compared in 5 randomized trials that have been conducted. None have shown an overall survival advantage for a longer course of therapy, and only 1 has shown an advantage in time to recurrence for a longer course. There has been a nonsignificant trend in some of the trials in favor of the shorter arms of therapy. It must be concluded at the present time that regimens that utilize 4 to 6 months of therapy are likely to be as effective and are probably preferable to 12 or more months of therapy.