Sixty granulocytopenic patients (granulocytes less than 1000/mm3) affected with solid tumors, previously submitted to antiblastic therapy and with infections, were treated with three antibiotic combinations: amikacin + ceftazidime, amikacin + piperacillin or amikacin + aztreonam. In 68% of the cases the infections were due to gram-negative and in the remaining 32% to gram-positive microorganisms. The results obtained with the three treatments show a slight but significant statistical difference (p less than 0.05), due to the greater efficacy of the amikacin + ceftazidime combination on gram-positive and amikacin + aztreonam on gram-negative bacteria.