This is a report on field trials near Lethbridge, Alberta, in 1954, to determine whether the artificial distribution of the bacterium Pseudomonas aeruginosa (Schroeter) Migula would contribute to the biological control of a natural population of grasshoppers. This bacterium was isolated from laboratory-reared grasshoppers, and Bucher and Stephens (1957) showed it to be relatively virulent when experimentally fed to grasshoppers but very susceptible to desiccation. Unpublished information from Miss Stephens indicated that the addition of sucrose (5.0 per cent), casein (1.0 per cent), and gastric mucin (1.0 per cent) to suspensions of P. aeruginosa helped to preserve the viability of the bacteria when dried in thin films. Therefore, these substances were incorporated in all formulations used in the field experiments.