[en] The azomethine derivatives 8-hydroxy-1-(2-hydroxy-1-naphthylbenzylideneamino)naphthalene-3,6-disulphonic acid (HSNHB) and 8-hydroxy-1-(2-hydroxy-1-naphthylmethyleneamino)naphthalene-3, 6-disulphonic acid (HSNHN) were synthesised. HSNHB gives no colour reaction with boric acid, but HSNHN reacts with boric acid and produces a compound with maximum absorbance at 445 nm (pH 4) in a 30% V/V methanol-water solution. Beer's law is obeyed between 0.25 and 2 μg ml^-1 of boron. The molar absorptivity at 445 nm is 8700 l mol^-1 cm^-1. Interferences from Fe³⁺, Al³⁺ and Cu²⁺ are avoided by adding EDTA. This method has been applied to the determination of boron in natural waters and vegetable matter with good accuracy. (author)