Aminoglycosides still play a major role int e treatment of severe infections, especially those due to Gram-negative bacilli. They are usually administered together with a beta-lactam antibiotic, either to cover a wide antibacterial spectrum, or to obtain a better bactericidal effect, or to prevent the emergence of resistant mutants. They are mainly used in severe urinary tract infections and/or in those due to multiresistant organisms and in Gram-negative pneumonia and meningitis (intrathecally, since they poorly diffuse into the CSF). Combined with cephalosporins they constitute the first-line treatment of severe, life-threatening infections caused by Gram-negative aerobes. Given simultaneously with penicillinase-resistant semi-synthetic penicillins or with vancomycin they act synergistically against staphylococci and can be used initially for a few days in the treatment of severe staphylococcal infections. It is also for this synergistic action that they are combined with penicillin G or ampicillin in the treatment of endocarditis. The ototoxic or nephrotoxic effects common to all aminoglycosides can be avoided by adjusting the doses to the degree of renal function, by limiting their use to about a fortnight (except for endocarditis) and by monitoring blood levels.