Glutathione peroxidases and glutathione reductase activities are expressed from the early stage of Bufo bufo development. Selenium-dependent and selenium-independent glutathione peroxidase activities fluctuated independently. The activity of selenium-independent was found to be higher than that of selenium-dependent glutathione peroxidase through all stages of development. Glutathione reductase activity, after a slight fall from stage 4 to stage 7, constantly increased up to stage 25.