The LD50ofPseudomonas aeruginosa(Schroeter) Migula was significantly decreased when the bacteria were injected into or fed to grasshoppers along with 1% granular mucin. In feeding experiments on 490 treated and 490 control insectsP.aeruginosain mucin was 6.4 times (5% fiducial limits of 3.4 and 11.9) as potent asP.aeruginosaalone. Mucin did not appear to speed the death of the grasshoppers. The action by which mucin promotes the infection was not determined.