Urease (EC 3.5.1.5, urea amidohydrolase) was isolated from marrow cotyledons of 5-day old seedlings. The effect of exogenous phytohormones namely indolebutyric acid, naphthaleneacetic acid, indoleacetic acid, indolepropionic acid, indoleacetic acid and zeatin  at various concentrations (100-600 µmol) on urease activity in the cotyledons of marrow was investigated. The optimum concentrations of the five compounds that gave the highest activities of urease were 500 mol for  indolebutyric acid   indoleacetic acid, and 400 mol for naphthaleneacetic acid and indolepropionic acid  However, the optimum concentration for zeatin was 100 µmol .