A rapid and sensitive colorimetric method for the determination of thiamine propyl disulphide and thiamine disulphide, as pure drugs and in their respective dosage forms, has been developed, which is based on a colour reaction with 2,6-dichloro-p-benzoquinone-4-chlorimine in the presence of methanolic hydrobromic acid in a chloroform medium. The colours produced from thiamine propyl disulphide and thiamine disulphide have absorbance maxima at 445 and 460 nm, respectively. The concentration range for Beer's law compliance is 0–5.75 µg ml^–1 for thiamine propyl disulphide and 0–12 µg ml^–1 for thiamine disulphide. The method can be applied to the analytical control of thiamine propyl disulphide and thiamine disulphide in dosage forms with simple matrices, but when other compounds carrying an amino group are present a separation is necessary as the proposed colour reaction is a general one for all such compounds. The removal of riboflavine and analgin, present in some of the currently available commercial formulations of thiamine propyl disulphide and thiamine disulphide, was found to be necessary and is described.