The saturation magnetization and switching characteristics of amorphous Fe 7 7 . 5 Si 7 . 5 B 1 5 fibres were investigated after hydrogen incorporating by the electrochemical method. The switching field (H * ) increased from its as-received value (5.57 Am - 1 ) to 18.62 Am - 1 after charging with a current density (I C h ) of 30 mA cm - 2 for 2 h. The saturation magnetization (M s ) decreased with hydrogen content up to a critical concentration corresponding to I C h = 60 mA cm - 2 after 2 h of charging. At this critical current density, M s decreased from 1.57 T, its as-received value, to 0.89 T. The results are explained by considering various kinds of interaction of hydrogen with metals, such as electron exchange, volume dilation, etc.