Marshall, Emerson and Cutting 1 have emphasized that the distribution of sulfanilamide is essentially equal in all the tissues of the body with the exception of bone and fat. They called attention to the slightly lower concentration of this substance in the saliva and pancreatic juice of the dog and in the spinal fluid of man as compared with its level in the blood. These workers studied the concentration of sulfanilamide in pleural fluid in a few instances. They found, for example, a level of 7.4 mg. of drug per hundred cubic centimeters of pleural exudate in a case of streptococcic empyema, with a corresponding blood level of 9.3 mg. per hundred cubic centimeters. In another case they found 11 mg. per hundred cubic centimeters in a pleural effusion from a patient to whom 0.10 to 0.12 Gm. of drug per kilogram of body weight was being administered daily. In