By use of the subcutaneous route, chronic Pseudomonas aeruginosa infections were established in normal mice undebilitated by burn wounds or leukopenic agents. Using a 21-day holding period, an LD50 value of 4.6 times 10(8) colony forming units was obtained. After subcutaneous infection, the dermis was completely necrosed with the lesions reaching deep into the subcutaneous tissue and musculature within 3-4 days. Ecthyma gangrenosum-like skin lesions at the site of infection appeared during this time period. By 7-15 days all mice exhibited a systemic infection. Both the livers and lungs showed a great deal of hemorrhage and frequently contained large necrotic foci, while the kidneys showed petechial hemorrhage and occasional renal abscesses. The susceptibility to infection was markedly increased by use of various antineoplastic agents and suprarenal hormones. However, the type of tissue damage or severity was not significantly altered as compared to infected mice which had not received any of the chemical agents.