The nature and distribution of the various combinations of chromosome configurations generated at prophase of meiosis is estimated in two somatic hybrids derived from the same fusion experiment (SH2 and SH17). The number of cells displaying particular combinations is compared with the number expected, on the assumption that the 12 sets of six chromosomes within the hybrid complements behave independently of one another. In SH17 the sets do behave independently of one another. The probability of any particular configurations occurring within one set is the same as for those configurations occurring in any of the other sets of chromosomes. In SH2 this is not so. Some particular configurations are more likely to occur in some chromosome sets than others. Evidence is presented that suggests that the difference in the distribution of chromosome configurations in SH2 and SH17 is caused by a difference in chiasma frequency, probably resulting from a mutation affecting chromosome behaviour. Such variation between the two hybrids, albeit derived by somatic hybridization from the same parents, clearly has implications for their potential value as breeding material.