The compound barbitone, and the related compounds amylobarbitone, butobarbitone, hexobarbitone, phenobarbitone and quinalbarbitone, have been determined by catalymetric-thermometric titration involving an acid-base reaction in the analyte followed by a base-catalysed indicator reaction. The base-catalysed reactions used were the dimerisation of acetone and the polymerisation of acrylonitrile with dimethylformamide as a matrix diluent. The effects of excipients are reported, and a method of assay of dosage forms is proposed.