Wine yeast strains are characterized by a high chromosomal DNA polymorphism. This can be explained partly by a size difference of different variants of specific chromosomes. This difference can reach up to 45% of the size of the chromosome in question. Two strains, SB1 and Eg8, have a very complex chromosomal pattern and show one band hybridizing with probes from two different chromosomes derived from a reference strain. This is an indication of the presence of "hybrid" chromosomes in these wine strains. The most astonishing result concerns chromosome VIII, frequently present in wine strains in two variant forms. The first normal form has a size of about 580 kb while the second is around 1000 kb. These two forms segregate at meiosis and recombine with a normal chromosome VIII from a laboratory strain. Wine yeasts are thus very different from haploid laboratory strains.