The U. S. P. assays for acetylsalicylic acid and its tablets are not universally applicable to these dosage forms containing buffers, flavoring agents, coloring materials, and enteric coatings. The U. S. P. test for free salicylic acid is not quantitative and may be subject to error unless additional controls are provided. A method of assay is presented which is applicable to tablets containing the usual excipients used in the preparation of plain, buffered, enteric coated, and children's tablets. A quantitative procedure for the determination of free salicylic acid is also recommended.