Vitamin B₁(thiamine) was found to give one anodic peak and three anodic peaks by cyclic voltammetry at a planar glassy carbon electrode, when treated with 0.1 mol dm^–3 sodium hydroxide for 5 and 30 min, respectively. The reverse cyclic voltammograms did not show any cathodic peaks. The electro-active form of thiamine was subjected to cyclic voltammetric studies under a variety of solution conditions. The effect of pH was investigated over the range pH 7.0 to 12.5. The magnitudes of the αn_a values suggested that the initial oxidation reaction of thiamine involved the loss of one electron and the product of this reaction is likely to be a disulfide. The electrode reaction was found to be adsorption-controlled when only phosphate buffer was used. However, when acetonitrile was added to this supporting electrolyte at concentrations of 17.5 and 20% v/v the peak current became diffusion-controlled. A convenient and rapid method of analysis for two different multivitamin tablet formulations was developed. After a simple pre-treatment procedure, extracts were analysed using HPLC with a wall-jet amperometric detector. The results of the analyses suggest that the proposed method has promise for the routine determination of vitamin B₁ in the products examined.