The evolution of magnetic properties and structure with annealing temperature of glass-coated microwires with composition Fe73.5B22.5SixCu1Nb3 (x = 11.5, 13.5 and 16.5) has been studied for samples with diameter of metallic nucleus ranging from 4 to 22 mu m and fixed total diameter of around 26 mu m. Magnetic bistability characterized by a single and large Barkhausen jump is observed in all the cases in the as-obtained state as well as after devitrification into nanocrystallized state (annealing at around 550 degrees C), while this bistable character is finally lost after annealing at around 750 degrees C when the final second crystallization stage proceeds. It is noticeable that squared loops can be observed in the range of switching field values between I and 100 Oe, depending on the structure of the material with the consequent possibility of tailoring the magnetic bistability. Copyright (C) 1996 Acta Metallurgica Inc.