Fluorochrome-labeled oligonucleotides ( n = 44) corresponding to mouse genome repetitive sequences were hybridized in situ with pachytene nuclei of mouse spermatocytes. Signals of the repetitive sequences MaLR, MER, and (GT) were found to be dispersed through chromatin, and signals of B1 repeats and minisatellites were mostly attached to synaptonemal complexes immunostained with anti-SYCP3 antibodies. These results suggest that B1 repeats and minisatellites are candidates for sequences anchoring chromatin to synaptonemal complexes.