This paper presents results concerning the effect of cobalt substitution on bulk (thermal) and surface (electrochemical) properties of Finemet type alloys. Thermal properties of the alloys were determined by differential scanning calorimetry (DSC). The partial substitution of iron for cobalt up to 10 at.% improves the stability of the alloys. The results obtained using various electrochemical techniques show that the new component does not improve notably the electrochemical characteristics of the basic composition alloy sample in KOH solutions. On the other hand, the high corrosion rate registered in HCl solutions does not allow us to obtain quantitative data. (C) 2003 Elsevier Ltd. All rights reserved.