The method consists in acetylating the hydroxyl groups containing compounds with a mixture of acetic anhydride and pyridine. The excess of acetic anhydride is hydrolized and the acetic acid formed is titrated with a potassium hydroxide solution. Primary and secondary alcoholes are acetylated completely by this method. Phenols, anthranilates and aldehydes are acetylated either completely or partially. Tertiary alcohols are acetylated only in a negligible extent.