Since experimental evidence shows that lethal doses of isoniazid (isonicotinic acid hydrazide) result in liver damage,1it is to be expected that one of the possible clinical observations might be evidence of this condition in patients treated with this drug. Liver function studies have been included in the clinical observation of many hundreds of such patients.2So far, studies of patients on dosage schedules in use at this time, from 2 to 8 mg. per kilogram of body weight,3have failed to reveal demonstrable evidence of toxicity to the liver, and no reports of the occurrence of jaundice have been presented. The following case report may therefore be significant. REPORT OF A CASE The patient was a 46-year-old man whose chief complaint was of jaundice. His history included right rib resection for empyema in 1927 and, after left pleural effusion was diagnosed in 1932, the left side