Suspensions of B. metiens in dist. water were heated to 80[degree]C. for 10 min. to kill vegetative cells, and 1 ml. was added to 99 ml. of the proper dilution of alkyl dimethyl 3,4-dichloro benzyl am-monium chloride (Tetrosan). The tests were made at 20[degree] at pH 7. A 1:10 dilution of Tetrosan killed B. metiens when tested by the FDA method. A large number of spores (60-75%) were killed almost immediately with a subsequent marked reduction in the rate of killing. The results of expts., with Tetrosan and cetyl trimethyl ammonium bromide, against Staphylococcus aureus paralleled those obtained with spores. The killing dilution was about 1:50,000 as detd. by the FDA method, but over 90% of the organisms were killed immediately by dilutions as low as 1:300,000,.