Adventitious shoot regeneration was observed using leaf-petiole explants from shoot-proliferating cultures of 'Comet' red raspberry (Rubus idaeus L.). A maximum regeneration rate of 70% (3.7 shoots/explant) was obtained using 4.5-9.1/xM (1-2mg1-1) N-phenyl-N'-l,2,3-thiadiazol-5-ylurea (thidiazuron or TDZ) with 2.5-4.9/xM (0.5-1mgl 1) 1H-indole-3-butanoic acid (IBA) or 2.3 IxM (0.5 mg 1-1) TDZ with 4.9/xM (1 mg 1-1) IBA in modified Murashige-Skoog medium. TDZ was more effective than N-(phenylmethyl)-lH-purin-6-amine (BA) at promoting regeneration in combinations tested with IBA (maximum 50% regeneration rate; 1.8 shoots/explant). Variation in the agar concentration or incubation temperature, orientation or scoring of the leaf-petiole explants and use of separate leaf or petiole explants had no effect on shoot regeneration. Incubation in the dark for 1, 2 or 3 weeks prior to growth in the light did not influence the percent regeneration rate but depressed the number of adventitious shoots. Explant source, from micropropagated shoots or greenhouse-grown plants, had an effect on shoot regeneration that was genotype dependent. Only 8 of 22 (36%) raspberry cultivars were capable of regeneration from leaf explants derived from greenhouse-grown plants.