The incidence of nosocomial infections is studied retrospectively, among 174 patients with a chronic respiratory disease, in a ICU during one year (1987). The medium-age is 65 years (range: 19-87 years); the sex-ratio is 125/50 (men/women); 88 (50%) are ventilated; 48 (27%) meet with a nosocomial infection during their stay in the unit. This superinfection involve 61% of the deaths. The lung involved in 67% of the cases, a septicemia from a venous catheter is found in 18% and an infection of the urinary tract in 15%. The nosocomial pneumonias are always the outcome of the ventilation. The Gram-negative bacilli are the most frequent, particularly Pseudomonas aeruginosa (44%). The initial gravity promote the superinfection (SAPSE with superinfection: 16.63 +/- 5.67/without 11.43 +/- 4.59 p less than 0.001). The superinfection involve a prolongation of the ventilatory time (with 27.52 +/- 31.14 days/without 7.27 +/- 7.05 days p less than 0.001). The gravity and the frequency (28%) of the nosocomial infections set the problem of the antibioprophylaxis.