Round paper discs soakedin pure biocide or its corresponding 10 vol.% aqueous solution were set on a solidified agar culture medium inoculated with a solution of a selected microorganism. The four microorganisms studied, usually involved in food preservation and water pollution control processes, were: Aspergillus niger (fungus–mould) (wild strain),Candida kefyr (fungus–yeast) (wild strain), Bacillus cereus (bacteria gram-positive) CECT131 and Escherichia coli (bacteria gramnegative) CECT434.