Commercially available 7075 and 7050 alloys showed environmental degradation in ductility accompanied by intergranular fracture when tested at a relatively slow strain rate of 10(-7)/s in laboratory air. The degradation or embrittlement became severe with the increase in relative humidity of the testing environment. In every case, the embrittlement of the 7050 alloy was more serious than that of the 7075 alloy. Laboratory-made X7075 alloy which had the same amount of major solutes with the 7075 alloy but containing Zr in place of Cr revealed that additive Zr enhanced the environmental degradation of Al-Zn-Mg-Cu alloys.