The macrocyclic trichothecenes are a group of potent protein synthesis inhibitors that have been encountered in indoor air and food as a result of infestation by the fungus Stachybotrys. To evaluate the capacity of these mycotoxins to alter immune functions, the effects of satratoxin G, H, F, roridin A, and verrucarin A on interleukin 2 (IL-2) production and viability were evaluated in a murine T-cell model. EL-4 thymoma cells were stimulated with phorbol 12-myristate 13-acetate and ionomycin and concurrently exposed to various concentrations of the trichothecenes. Enzyme-linked immunosorbent assay (ELISA) of supernatants revealed that IL-2 concentrations at 24 and 72 h were significantly increased in cultures that were incubated in the presence of 0.5 to 1 ng/ml of satratoxin H, 1 to 5 ng/ml of isosatratoxin F, 0.1 to 0.5 ng/ml of roridin A, and 0.25 to 0.5 ng/ml of verrucarin A. However, IL-2 levels at these time points were significantly depressed when incubated in the presence of higher concentrations of satratoxin G ( 2.5 ng/ml), satratoxin H and isosatratoxin F ( 5 ng/ml), and roridin A and verrucarin A ( 1 ng/ ml). Cell viability, as measured by the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay, was depressed by each of the trichothecenes in a concentration-dependent manner. MTT responses were significantly decreased by as little as 0.5 ng/ml satratoxin G, roridin A, and verrucarin A and by 2.5 ng/ml of isosatratoxin F and satratoxin H. When these data were compared to those found in EL-4 cells for the 8-ketotrichothecene vomitoxin ( deoxynivalenol) , a common food contaminant, the macrocyclic trichothecenes were at least 100 times more potent. The results indicate that, at low concentrations, macrocyclic trichothecenes as a group could superinduce IL-2 production even while partially decreasing cell viability, whereas higher concentrations suppressed cytokine production and were markedly cytotoxic. The capacity of these compounds to dysregulate cytokine production in a biphasic fashion may play an etiologic role in outbreaks of human illnesses associated with indoor Stachybotrys contamination.