Developing parthenogenetic eggs of Daphnia magna were used as a test-system to evaluate the effect of a number of low-frequency electromagnetic fields (EMF) of 75microT density. Two blocks of EMF acting frequencies were found in the studied series-45, 110, and 175Hz, and 435 and 500Hz. Developing parthenogenetic eggs of D. magna exposed to EMF with indicated parameters have shown accelerated rates of embryonic development. Females that developed from exposed eggs have shown deteriorated production characteristics in their first brood. Used test-system may be successfully utilized to detect weak effects directly during embryogenesis. However, results obtained only during daphnids' early developmental stages are incomplete without observations on their further development.