A new method for the determination of nitrogen in biologic material is described. It is based on an improved ashing procedure and the Berthelot reaction in which nitrogen is converted to indophenol. The concentration of this substance is determined photometrically. The proposed method yields the same results as the Kjeldahl procedure; however, it offers a higher degree of sensitivity combined with the same degree of accuracy. In addition, the determination requires only 4 hr., in comparison to 24 hr. for the Kjeldahl method.