The potential for plant growth regulator (PGR) manipulation of `Chester Thornless' blackberry (fibus spp.) primocane growth was evaluated. PGR treatments included combinations of soil-applied uniconazole at 1, 5, 25, and 125 mg/plant and GA, foliar-applied one or two times at 100 ppm 3 and 4 weeks after a 25-mg/plant uniconazole application. Also, GA and BA were applied at 100 ppm alone or in combination one, two, or three times. Increasing rates of uniconazole reduced primocane length, leaflet count, and leaf, cane, and root dry weights. GA, applications reduced primocane length and increased branch elongation but failed to reverse the effects of uniconazole at 25 mg/plant, except those on branch length, leaflet count, and primocane dry weight. Only applications of BA + GA, increased both branch production and elongation and dry weights of some component tissues, while BA alone generally had no effects. Chemical names used: (E)-1-(p-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-1-penten-3-ol (uniconazole); N-(phenylmethyl)-1H-purin-6-amine (benzyladenine, BA); gibberellic acid (GA).