In both adults and children RU 41740 exerts an immunomodulating effect and prevents recurrent respiratory infections. Patients with such infections frequently consult for acute episodes, and it was deemed necessary to evaluate the safety of the drug given concomitantly with antibiotic in acute infections. Three double-blind, drug versus placebo studies were conducted in fragile institutionalized or hospitalized patients. Antibiotics were administered simultaneously with RU 41740 in one group and with a placebo in another group. The studies performed by Albarede and Ollivier showed that in acute respiratory infections RU 41740 was well tolerated and resulted in a more rapid improvement of severity score. Grassi and al. studied chronic bronchitis patients admitted for acute on chronic episode. RU 41740 produced a more rapid improvement in the most severely ill patients, and it was well tolerated. It is concluded that RU 41740 can be initiated safely in acute episodes occurring in subjects with recurrent respiratory infections, and that it results in a faster improvement of clinical symptoms.