A colorimetric method using the azomethine H reagent is described for determining boron in an acid extract of plant tissue ash. The method consistently gave the certified value of 33±3 ppm B for NBS orchard leaf reference material No. 1571 with 3.2% coefficient of variation. Samples were dry ashed and the ash extracted in 10 ml 0.36 N H2SO4for 1 hr. at room temperature. Several acidic extractants and extracting conditions were compared which gave the certified value, but involved heating and readjusting the final volume.