An enzyme immunoassay (EIA) system for the detection of L. pneumophila antigen in clinical material (sputum, urine, bronchial washings) has been developed. The use of EIA permits the detection of L. pneumophila antigen in the urine of 75-80% of patients during the first week of the disease. The specificity and sensitivity of EIA makes it possible to recommend this method for the rapid diagnosis of L. pneumophila infection.