A ‘crumbly fruit’ condition is sometimes found in raspberry cultivars. In ‘Malling Promise’ this is associated with a change that occurred early in the cultivar’s history and was perpetuated by intensive vegetative propagation. Results from investigation of the condition in ‘Norfolk Giant’ failed to show whether an observed chromosome change or virus infection was the cause. Some of the results for ‘Malling Promise’ were similar to those for ‘Norfolk Giant’, but in ‘Malling Jewel’, and possibly in ‘Latham’ too, there is evidence that the condition can be caused by mutation of the dominant allele at a heterozygous gene locus to give the homozygous condition for a recessive gene affecting fertility. This gene appeared to he linked in a chromosome segment which forms part of a balanced lethal system, and this probably helps to maintain its frequency. Checking the fertility of material used for propagation is suggested as a means of reducing the incidence of crumbly fruit.