Groups of BALB/c mice were treated with a sub-lethal dose (60 micrograms) of staphylococcal enterotoxin B (SEB) intraperitoneally and were sacrificed at 2, 5, 8, or 10 h post-injection. Organ, blood plasma and lymph node samples from these mice were analyzed. Plasma levels of urea, creatinine and alanine aminotransferase were significantly raised above normal by 5 h post-injection. However, alkaline phosphatase levels showed an erratic increase after toxin administration and, after administration of 10-40 microgramS SEB per mouse, were consistently at least 30% below normal levels at 24 h post-injection. Weight change was also monitored but found to be inconsistent. Lung, spleen and kidney samples appeared normal on histopathological examination, but liver samples showed minor polymorph infiltration and congestion. TNF-alpha, and IL-1 alpha levels in the plasma were raised by 8 h to picogram levels per ml of plasma, whereas IFN-gamma and IL-2 were raised by 2 h to nanogram levels per ml of plasma. Lymph node cells taken from mice treated with toxin were given a secondary stimulation with toxin in vitro. Although the response of the cells was lower than normal on assay at four days, a time response curve showed a peak in cell responsiveness to secondary stimulation with toxin at three days. These data indicate that biochemical markers and cytokine levels are affected by the administration of SEB to mice and may be used as indicators of toxicity.