The seleno-organic compounds are highly active in several anti-inflammatory assays performed in mice and rats. However, they differ from the classical non-steroidal anti-inflammatory drugs including indomethacin despite the fact that both types of drugs are inhibitors of prostaglandins and leukotrienes. Furthermore, ebselen and analogs are potent anti-oxudants in many animal cell cultures. The toxicity of the drugs is low because selenium in their structure is not bioavailable. We have discovered that the seleno-organic compounds induce interferon gamma tumor necrosis factor alpha and other cytokines in human peripheral blood leukocytes (PBL). Furthermore, the action of the drugs and PHA or Con A was synergistic. However, ebselen and analogs were found to be inactive as the cytokine inducers in cultured rat or mouse lymphoid cells. In cotrast to their effects in human PBL, the drugs even inhibited the production of IFN-gamma after stimulation with PHA or Con A. The inhibition was dose dependent. We suggest that the induction of IFN by ebselen and analogs is species specific and it may depend on interaction of the drugs with a specific receptor and/or signal-transducing system present in human but not in some animal cells.