A controlled study was performed to evaluate the efficacy of human hyperimmune plasma (HIP) for protecting burned mice from Pseudomonas infection. The HIP was prepared from healthy volunteers immunized with endotoxin protein (Ep) of Pseudomonas aeruginosa. It contained antibody against Ep up to the titre higher than 1:128. Mice with full-thickness burn of 13% TBSA, infected by subeschar injection of 0.2 ml P. aeruginosa (CFU/ml), were treated with HIP at 6 hrs and 18 hrs postburn. The survival rate of the former on the 7th day was 45%, while in mice treated with normal plasma (NP) was 14% and in control mice 10% (P < 0.01). If the HIP was given 18h after burn, the survival rate was 43%, while in mice with NP was 39% and in control 42% (P > 0.05). The results indicate that HIP is able to protect burned mice from Pseudomonas infection giving at 6 hrs postburn (pre sepsis) but not at 18 hrs postburn (post sepsis).