A double blind study on BALB/c mice was conducted to examine the effects of extremely low-frequency electromagnetic fields on fertility. The mice were continuously exposed or sham-exposed from conception for two generations to magnetic fields varying between 0.5 and 77 muT. Biological parameters related to fertility were evaluated. Serum testosterone levels and mass of testes and adrenals were determined. No significant difference was found between the sham-exposed and exposed groups for all the biological endpoints, except for sperm motility. A significant difference between the two groups was found prior to the swim-up test with quantitative analysis of sperm motility as well as after the swim-up test for quantitative and qualitative analysis of sperm motility. ELF-EMFs significantly decreased the number of living sperm and the quality of movement of sperm, although these adversities did not impact on the outcome of the other parameters investigated.