A total of 101 patients with advanced breast cancer were treated during the years 1976 to 1978 with doxorubicin, vincristine and cyclophosphamide, and randomized to receive either levamisole or placebo in a double-blind fashion. The chemotherapy cycles were repeated every four weeks, and levamisole, 2.5 mg/kg, was given on two consecutive days every week except on the days chemotherapy was given. The patients treated with levamisole exhibited higher response rates (63%) than patients given placebo (47%). The survival rate was also significantly higher in the levamisole group. The results correlated with potentiation of intracutaneous PPD test. In the lymphocyte blast transformation tests, the suppression of T-cell response to mitogens two weeks after the start of chemotherapy was markedly diminished by levamisole. In contrast to some negative reports, the results of the present study are encouraging for further evaluation of levamisole and other biological response modifiers in breast cancer.