Explants from five clones of Quercus robur (three of juvenile origin and two from adult trees) were cultured on Gresshoff and Doy medium supplemented with 0.2 mg l(-1) 6-benzylaminopurine. Shoot proliferation from apical and nodal segments was influenced by both clone and type of explant. To increase the efficiency of the propagation procedure, donor shoots (20-25 mm in length and with 2 mm removed from the tip) were recultured at 4-week intervals, and the newly formed shoots harvested before each transfer. Under this regime, the multiplication coefficient (proportion of explants forming axillary shoots multiplied by the mean number of new 8-mm stem segments per explant) was greatest for the second crop and declined sharply by the fourth or fifth crop, in three of the four clones tested. Successive additions of fresh liquid medium to old cultures was much less effective than transfer to fresh medium in promoting axillary shoot production. Elongation of shoots before rooting was increased significantly (P < 0.05) in one of two clones tested by transfer to a medium containing either 0.1 or 1.0 mg l(-1) of zeatin. Addition of fresh liquid medium containing zeatin to old cultures failed to improve shoot elongation or axillary shoot production. However, treatment for 15 days with liquid medium containing 0.1 or 1.0 mg l(-1) indol-3-yl-acetic acid increased subsequent rooting.