Investigations related to the development of an experimental renal porphyria in Syrian Hamsters include analyses of porphyrins and their biosynthetic enzymes, as well as of renal functional implications of this "new" condition. Major emphasis will be given the study of renal cortical functions, including erythropoietin formation, tubular absorption, and blood pressure regulation. Study of pigment labelling following intravenous injection of double or triple labelled precursors (i.e. ALA-H3, glycine-C14, and glycine-N15) in patients and normal volunteers will continue, as will studies of the isolation and characterization of normal urinary ("urochrome") pigments, circadian patterns of porphyrin excretion, and methodological improvements.