Effects of abscisic acid on radicle protrusion, oxygen uptake and total RNA synthesis were investigated. It was found that ABA had no effect on oxygen uptake before radicle protrusion. RNA synthesis was only inhibited by ABA after 9 hours of imbibition. Extrapolation of radicle protrusion time curves from seeds treated with various concentrations of ABA suggested that ABA did not affect the initiation of cell extension, but inhibited growth of the radicle.