There are five aspects of the proposed research: 1. To separate, identify and quantitate unchanged hydralazine and its major metabolites in urine and, to the maximum extent practical, in blood and solid tissues. The initial work will be with hydralazine-1-C14 in rats, using the chromatographic techniques of McIsaac & Kanda. 2. To seek differences in hydralazine metabolites in the urine of rats as a function of hydrazaline exposure and in the urine of rabbits as a function of acetyl transferase activity. Differences in metabolites will also be sought in urine of hydralazine-treated animals as functions of ANA, LE cells, or other induced changes in circulating cells or proteins. 3. To seek specific antibodies to hydralazine and to its metabolites in exposed animals, concentrating particularly on any metabolites which are found in association with high exposure, with autoimmune or other changes in circulating cells or proteins, or with "slow acetylation." The metabolites will be attached to sheep red cells via bis-diazotized benzidine in a modification of Friedman and Heine's method. 4. To seek differences of hydralazine metabolites in the urine of hypertensive patients treated with hydralazine. Correlations will be sought with hydralazine exposure, race, acetylation rate, autoimmune changes, other hydralazine-induced chemical abnormalities, and symptomatic hydralazine toxicity. Ten patients with a history of hydralazine toxicity will be similarly studied. 5. To investigate whether a. hydralazine induces urinary loss of pyridoxine and whether such loss is related to acetylation rate or other variables considered above; b. there are characteristic hydralazine-induced changes in urinary trace metals associated with any of the variables considered above; c. the efficacy of blood pressure control can be correlated with either the urinary pattern of hydralazine metabolites or with antibodies to them.