FI and F2 hybrids were produced using three winter wheat varieties (Bernina = biscuit wheat, Arina and Forno = bread wheat) and two spelt cultivars (Oberkulmer and Rouquin). Data are based on field trials in 1989 and 1990. All the combinations tested gave a very high relative heterosis on grain yield per ear, varying between 29.9% and 47.6% with an average of 42.1%. Even the higher parent was outyielded by 24.1% to 45.7%. This was the result of a heterosis effect on the two yield parameters grain number per ear and single grain weight. In the F2, heterosis for grain yield per ear was not significant with a range between 3.9% and 12.0%. F1 hybrids showed a heterosis effect on plant height but no hybrid was taller than the spelt parents. These data show that the gene pool of spelt could be potentially usefull for the selection of parents for hybrid production. For practical applications there remain several problems to be solved. Despite the very high heterosis effect the yield potential of spelt needs to be improved. No short spelt varieties exist at present to produce hybrids short enough for commercial application. Technical problems in the seed production arise because of the close tightness of the spelt glumes hampering either the pollination by the wheat parent or the pollen dispersal if used as a pollinator. However, a breeding effort to select for improved parents within the gene pool of spelt appears useful for future F1 hybrids between spelt and wheat.