Previous experiments have shown that Pseudomonas aeruginosa may infect the middle ears of chinchillas by way of the eustachian tube and that chinchillas with acute otitis media (AOM) are more susceptible to pseudomonas infection than animals without AOM. The purpose of this experiment was to examine the effects of otitis media with effusion (OME), induced by means of eustachian tube obstruction, on middle ear susceptibility to nasal inoculation of P. aeruginosa. Chinchilla eustachian tubes were obstructed with silicone rubber sponge bilaterally; OME developed in eight animals (11 ears) three bilaterally and five unilaterally and persisted for 6 months. Ten chinchillas with normal eustachian tube function served as controls. All animals were nasally inoculated with 5 times 104 colony-forming units of P. aeruginosa. Pseudomonas otitis media developed in eight of 11 OME ears with effusion, none of five ears without OME, and four of 20 control ears (X2 = 11.782, p = 0.003). Therefore, P. aeruginosa can infect the middle ear by way of the eustachian tube. Tubal dysfunction may lead to the development of chronic suppurative otitis media by increasing tubotympanic susceptibility to opportunistic pathogens.