SummaryAdministering triamcinolone, 1 mg kg-1 24 h-1, results in increased ammonium excretion which resembles that observed during acid loading. This increase cannot be attributed to tubular ion exchanges or potassium depletion but, rather, is due to triamcinolone's effect upon renal ammonia production. The three- to fourfold increase in ammonia, glucose, and 14CO2 production is consistent with glucocorticoid mediation of the mitochondrial glutaminase I activation.I am indebted to Dr. M. Chretien, Director of Protein and Pituitary Hormone Laboratory of the Clinical Research Institute, for reviewing this manuscript, and to the excellent secretarial assistance of Misses Carole Tremblay, Anne Lesperance, Mrs. Anne Masseau, and Linda Paquette.