prospective, randomized, single-blind study comparing two groups of patients treated with aerosolised (AS) colistin versus colistin intravenously (IV). Included were patients who have mechanical ventilation over 48 hours and that have developed a VAP. A VAP was defined as a CPIS (Clinical Pulmonary Infection Score) >6. Exclusion criteria were septic shock and/or bacteraemia. Included patients were divided into two randomized groups. The 1st received colistin in AS as 4 MU by nebulisation 3 times per 24 h. The 2nd received colistin in IV as a loading dose of 9 MU followed by 4.5MU two times per 24 h. Colistin was given for 14 days or until extubation. Patients were followed for 28 days. Therapeutic efficacy was assessed by a primary outcome: the cure of VAP at day 14 of therapy and defined as resolution of clinical and biological signs of infection that means a CPIS< 6 and bacteriological eradication. Secondary outcomes: duration of mechanical ventilation, ICU stay-length and mortality at day 28. Systemic toxicity was assessed by the occurrence of acute renal failure (ARF) defined as increase of plasma creatinine more than 1.5 times its base value.