The need for more effective and potentially less toxic antimicrobial agents than aminoglycosides for treatment of gram negative bacilli pneumonia specially Pseudomonas aeruginosa, explains the interest for experimental models of pneumonia. These models allow to study the efficacy and safety of antibiotics alone or in combination. Aminoglycosides and new quinolones are more effective than beta-lactams for life threatening infection with high inoculum, the only exception to this finding has been for N-formimidoyl thienamycin, whereas for less severe infections aminoglycosides and beta-lactams are equivalent in efficacy. In contrast to high inocula pneumonia, combining beta-lactams with aminoglycosides give additive of synergic benefits for treating low inocula. Experimental models allow to compare continuous versus intermittent administration of antibiotics, different regimens of the same antibiotics (single daily dose of aminoglycosides versus conventional administration) and new antiinfectious agents as anti-pseudomonas hyperimmune globulins.