The fist case of legionnaires' disease in Israel is described. In a previously healthy woman, the disease was manifested by a rapidly progressive pneumonia, which was unresponsive to conventional therapy. The diagnosis was confirmed by positive serologic tests and the demonstration of the responsbile microorganism in the patient's lung tissue. Legionnaires' disease should now be suspected in patients with unexplained severe pneumonia, even in countries in which this disease has not been previously recognized.