The relative growth rates, growth rates, and final size of tillers and main-shoot leaves, internodes, and ear of a freely tillering spring barley genotype were measured and compared with those of a non-tillering single-gene mutant. Leaf and internode growth and final size were greater in the non-tillering mutant. The differences, it is proposed, arise because of changes in internal competition for assimilates brought about by the absence of tillers. There was little difference in ear growth or size, possibly because of abnormalities of ear development, which resulted in fewer spikelets in the non-tillering genotype.