Single and double-gene Rht1, Rht2, Rht3, Rht1 + Rht2 and Rht3 + Rht2 isogenic lines of wheat in four parental rht varieties were grown in drilled yield trials at four sites in 1989. The same lines were also grown in 1988 together with hybrid genotypes from CHA (chemical hybridising agent) F1 production plots. In the inbred lines shorter than one metre, Rht alleles reduced total shoot biomass by shortening the straw; mass of straw per unit plant height was unaffected. Highest grain yield was obtained from plant heights between 70 and 100 cm. The Rht genotype achieving this stature varied according to parent varietal height. The hybrids grown allowed comparisons between intra- and inter-varietal crosses over a range of Rht genotypes. In F1 hybrids positive heterosis was observed for plant height, grain yield and mean grain weight. Highest yields were obtained from inter-varietal hybrids carrying one, two or three doses of Rht1 or Rht2 or one dose of Rht3. An Rht3/rht hybrid showed resistance to premature ?-amylase production during grain ripening.