The addition of thidiazuron (TDZ) to MS salts and vitamins, instead of benzylaminopurine (BAP) increased both the culture weight and the proportion of ash embryo hypocotyl explants that produced adventitious shoots. The concentration of BAP, but not that of TDZ also affected these parameters. Addition of 1-naphthalene acetic acid reduced culture performance, indolebutyric acid (IBA) was beneficial, and 2,4-dichlorophenoxyacetic acid had no effect. During both 1990 and 1991, rates of regeneration declined as the growth season progressed. Adventitious shoots, which were also obtained from hypocotyls from dried seeds, were established as proliferating shoot cultures following transfer to DKW medium with 5.0 mg l(-1) BAP, and the resulting shoots were rooted in half-strength Woody Plant medium with 1.0 mg l(-1) IBA.