The ability of six mixtures to neutralize glutaraldehyde, o-phthalaldehyde and peracetic acid was tested using four reference strains: Pseudomonas aeruginosa CIP A22, Escherichia coli CIP 54127, Staphylococcus aureus CIP 53154, and Enterococcus faecium CIP 5855. Glutaraldehyde was the hardest to neutralize, and peracetic acid the easiest. The most effective mixture was Tween 80 with sodium bisulphate, sodium thioglycolate, lecithin and cysteine, and the least effective was Tween 80, lecithin and histidine. The efficacy of the neutralizers may indicate a propensity loss of activity from interfering substances when disinfectants are used in practice.