Patients with thermal injury suffer a high incidence of infectious complications secondary to impaired host resistance. Nonspecific immunostimulatory agents are being tested increasingly for their ability to correct the postburn immunosuppression. By means of a burned guinea pig model, three such drugs--indomethacin, cyclophosphamide, and cimetidine--were tested for their ability to correct immunosuppression and prevent lethal infectious complications. The burned animals were challenged with Pseudomonas aeruginosa 1244 on the third postburn day. Neither indomethacin nor cimetidine altered the animals' clinical course. However cyclophosphamide, at a dosage of 2 mg/kg body weight/day, improved survival from 30% to 57% and prolonged mean survival time from 5.72 to 7.77 days. Cyclophosphamide, at a dosage of 15 mg/kg body weight/day, decreased mean survival to 3.63 days and percent survival to 0. These data show that treatment with cyclophosphamide could be beneficial in severe burn injury patients, but further work is necessary due to the dose-dependent nature of the drug.