THE NITROGEN-MUSTARD gases were developed during World War II. Since there has been little clinical experience with these gases, it is believed worth while to record the following detailed information collected on 8 casualties from 1149 (code) vapor. This (1149) is probably the most effective nitrogen-mustard. The conditions of these casualties resulted during the developmental operation of a pilot plant at Edgewood Arsenal, Md. Two other casualties were hospitalized for cutaneous burns, and 10 additional patients with minor complaints were treated in the outpatient clinic. Meanwhile the safety problems in the operation of the pilot plant were solved, and no further casualties appeared at this particular time. ANALYSIS OF CASES It was impossible to estimate accurately the casualty rate, because of variation in production schedule and shift of employees. The casualty rate appeared high in the opinion of the workers in the pilot plant, all of whom had previous experience