The effects of intravenous fat emulsion on ventilated normal, diseased or distressed lungs were studied. Forty-eight patients with different types of respiratory failure were divided into four groups. Group A was composed of the patients with a normal lung condition; group B, patients with infectious pulmonary condition and respiratory failure; group C, patients with COPD and respiratory failure; and, group D was composed of the patients with ARDS due to various causes. Five hundred milliliters of 10 percent fat emulsion was infused within 4 h as partial parenteral nutritional support. We concluded that intravenous fat infusion decreased PaO2/FIO2 and increased P(A-a)O2 and intrapulmonary shunt in the patients with ARDS, while it had little effect on the patients with infectious pulmonary disease or COPD. The infusion of fat emulsion had positive effects on the patients with normal lung condition with increased PaO2/FIO2 and decreased P(A-a)O2 and shunt.