The acetyl content of cellulose acetate can be determined by measuring, in the near infrared region of the spectrum, the absorbance due to the residual hydroxyl groups. Pyrrole is a suitable solvent, permitting the determination of the acetyl content of cellulose acetates of from 35 to 44.8per thousand acetyl. A statistical study of the accuracy and precision of the near infrared, Eberstadt and carbanilation methods of acetyl determination has been conducted. The near infrared method can be accurately calibrated; the precision is of the same order of magnitude as that of the Eberstadt method. The carbanilation method has limits of error about one half as great as the other two methods.