Aluminium, zinc and mild steel were subjected to influence of wild strain Bacillus mycoides for 2 years under laboratory conditions at controlled temperature and humidity. The microorganisms were isolated from the metal samples exposed under outdoor conditions in different regions of Lithuania. Electrochemical impedance measurements performed for both biotic and abiotic samples indicated microbially influenced corrosion inhibition for aluminium, corrosion acceleration for zinc and indifference for steel. The microbiological corrosion inhibition implied an environmentally friendly alternative of corrosion protection to toxic chemicals, application of which due to stricter environmental regulations tends to be increasingly restricted. (c) 2006 Elsevier Ltd. All rights reserved.