1. Gluconeogenesis from glutamine, fumarate, pyruvate, glutamine plus fumarate, and glutamine plus pyruvate, was generally higher at pH 7.1 than at pH 7.4 and 7.7, whereas ammoniagenesis did not depend on the pH of the medium. 2. The intermediates of the Krebs cycle decreased ammonia formation from glutamine, raising at the same time gluconeogenesis. 3. Arsenite, malonate, maleate, hydrazine and 2,4-dinitrophenol inhibited gluconeogenesis, and enhanced simultaneously ammonia formation irrespective of the pH of the medium.