Abstract: Diploid and tetraploid forms of Lolium multiflorum and Festuca pratensis were crossed under controlled conditions and after embryo rescue all four combinations of autoallotriploid hybrids were obtained. Male and female fertility and chromosome pairing at metaphase I of meiosis were studied in several plants from each hybrid combination. The hybrids with two genomes of L. multiflorum and one of F. pratensis (genomic formulae LmLmFp and FpLmLm) were male and female fertile while the hybrids with two genomes of F. pratensis and one of L. multiflorum had a reduced fertility (FpFpLm) or were completely sterile (LmFpFp). Chromosome pairing at metaphase I varied among hybrid combinations depending on their genomic composition. LmLmFp and FpLmLm hybrids had similar patterns of pairing (1.83I + 5.29II + 2.85III and 2.22I + 5.22II + 2.75III, respectively) but they differed from those of FpFpLm (3.65I + 4.65II + 2.68III) and especially from LmFpFp (4.78I + 5.87II + 1.49III). Conventional analysis of meiosis failed to explain the differences in chromosome behaviour and fertility/sterility levels between the autoallotriploid hybrids with two Lolium or two Festuca genomes.