The use as antimocrobial agents of organosilicon quaternary ammonium compounds of the formula: ##STR1## wherein m+n is 16 to 19, m is 1 to 6, and n is 13 to 17 or m+n is 20 to 23, m is 4 to 11 and n is 9 to 17; X is a halogen; and Y is a hydrolyzable radical or hydroxy group.