Forty commonly used inactivators, both simple substances and mixtures, were tested by a quantitative suspension test for the property of being non-toxic to the bacterial cell. Some inactivators proved to be too inhibitory, even for undamaged organisms, namely cysteine in concentrations of 1.0% and higher, 0.3% and 2.0% lecithin (both especially for P. aeruginosa), and the mixtures 0.3% lecithin/2.0% polysorbate 80/0.1% histidine/2.0% turkey-oil red (for St. aureus) and 0.3% lecithin/3.0% polysorbate 80/0.4% sodium laurylsulfate (for both test organisms).