Hybridisations carried out between a number of tetraploid wheats (Triticum turgidum (L) Thell. ssp. turgidum conv. durum (Desf.) MacKey, N. comb.) and rye (Secale) species revealed a range from high to low levels of crossability between them.Variation in crossability level was due to genetic variation, both in tetraploid wheat and rye. The presence of a significant (p < 0.01) interaction in crossability between tetraploid wheat and rye indicates that the genetic system governing crossability is more complex than previously described.It appears that the mutation(s) in wheat from high to low crossability with rye took place at least as early as the tetraploid level of wheat evolution.