Thermometric titrimetry allows the quantitative assay of pure 3,4-diaminopyridine or in pharmaceutical capsules by titration in water by hydrochloric acid. Satisfactory titrations with 99 p 100 recovery and 1 p 100 precision were obtained with amounts of about 4.5 x 10(-4) mel. Lactose and starch used as excipients in the capsules as well as gelatin which constitutes their matrix, did not interfere in the titration.