An improved colorimetric method for the determination of boron was developed by investigating the effects of temperature, time, reagent concentration and composition of the reaction mixture on colour development with azomethine-H. Among 15 ions studied, only fluoride, aluminum, ferric and cupric ions interfered with colour development at below 10,000 ppm in sample aliquot. Tolerable concentrations for these ions were 5,000 ppm fluoride, 3,000 ppm aluminum, 2,500 ppm cupric and 200 ppm ferric ion. The method accounted for known additions of boron to nomal hydrochloric acid extract of plant material, to hot water extract of soil and to effluent. Boron determinations in these samples and sewage sludge extract were in close agreement with results obtained by the carmine method. The proposed azomethine-H method was found advantageous since use of concentrated sulphuric acid is avoided and smaller variations in results and superior precision are obtained.