The progression of the prophase-I stage in Syrian hamster spermatocytes has been studies at different ages, from 12 to 41 days after birth. Two stages, leptotene and diplotene, were identified, which had not previously been described in the Syrian hamster using spreading techniques. The most interesting observations are the presence of heterosynapses and telomere associations in 2.5% of the cells studies, and of nucleolar filaments also in 2.5%. Connecting fibers are structures that establish different types of bridges between two or three synaptonemal complexes (SCs) or between the elements of a single SC. Heterosynapses and telomere associations consist in the partial pairing of the terminal regions of nonhomologous lateral elements. These phenomena can be observed both in the autosomes and in the sex chromosomes. © 1987 Dr W. Junk Publishers.