The influences of some ecological factors (ambient temperature, magnetic field, herbicides) on the sensitivity of fish glycosidase to in vitro action of Roundup were studied. Higher water temperatures can vary glycosidase sensitivity to Roundup in vitro, the force and direction of the effect depends not only on the rate of water heating, but also on the type of enzyme and substrate. The action of magnetic storms (in the frequency range 0-5 Hz) during early embryogenesis results in enhanced the sensitivity of glycosidase in the intestine of roach Rutilus rutilus (L.) fingerlings to Roundup. Chronic effect of herbicide reduces glycosidase sensitivity to Roundup in vitro.