The effect of a low-frequency (1 and 10 Hz) pulse electromagnetic field (PEMF) on permeability of erythrocyte membrane in 47 rats while being exposed to a 14-day head-down tilt (HDT) and in 60 control rats was studied. After exposure to PEMF (20 min, 6-24 mT) the rats were Na(+)-, K(+)-cotransport and Na+,Na(+)-metabolism, Na and K losses as well as specific activity of Na(+)-, K(+)-ATP in the erythrocytes have been measured. An ability of PEMF to inhibit an ATP activity by 20-30% and to increase the rate of ions loss from the cells has been revealed. Under HDT, these effects are preserved. The possible mechanisms of PEMF effect on an ionic permeability of the membranes are discussed.