Ten patients with AIDS and progressive cytomegalovirus disease were treated with ganciclovir and foscarnet concurrently. The patients had received ganciclovir and foscarnet monotherapy a median of 330 days before receiving combination therapy for a median of 80 days. Nine of the 10 patients responded to the combination. No electrolyte abnormalities were noted during combination therapy, but rates of neutropenia (relative rate, combination vs. ganciclovir, 1.99; P = .229) and thrombocytopenia (relative rate, combination vs. ganciclovir, 1.53; P = .616) were higher with combination therapy than with either drug alone. The relative rate of anemia was significantly increased with combination therapy compared with monotherapy (relative rate, combination vs. ganciclovir, 2.69; P = .025). These data suggest that combination ganciclovir and foscarnet therapy after failure of either alone appears to be as effective as standard therapy with single agents. The rate of anemia with combination therapy was significantly greater than either agent alone, but no significant difference was noted among the other parameters of toxicity studied.