Abstract Investigations of [male] meiosis in silver fox X blue fox hybrids revealed meiotic arrests at the 1st prophase stage. Synaptonemal complex analysis using light and electron microscopy demonstrated the occurrence of multivalents, bivalent-like structures and unpaired axes. It was concluded that the sterility of [male] hybrid foxes is probably due to pairing problems of chromosomes caused by extensive karyotypical differences between the 2 species, resulting in unpaired chromosomes, chromosome segments and broken chromosomes.