Interleukin-1 (IL-1) plays a major role in the response to infection, inflammation, and immunological challenge. Eosinophils participate in the host response to parasitic infection and allergic and hypersensitivity diseases. The role of IL-1 in these disease states has not been extensively explored. We have reported that purified human monocyte derived IL-1 (mIL-1), a mixture of the two IL-1 forms but predominantly consisting of IL-1 beta, modulates eosinophil oxidative metabolism and enzyme secretion. Although the two major species of IL-1 (IL-1 alpha and IL-1 beta) have identical specific activities on T cells, we now report the selective effects of human recombinant IL-1 (hrIL-1) alpha and hrIL-1 beta on eosinophil function. Whereas hrIL-1 beta caused a significant increase in arylsulfatase secretion (235.4 +/- 29% of resting secretion, P less than or equal to .01) and beta- glucuronidase secretion (135.8 +/- 9.6% of resting secretion, P less than or equal to .02) similar to our experience with mIL-1, hrIL-1 alpha had no effect on enzyme secretion. However, a mixture of hrIL-1 alpha and hrIL-1 beta reproduced the ability of mIL-1 to inhibit the oxidative response to suboptimal doses of phorbol myristate acetate (PMA). When eosinophils were separated into subpopulations by density gradients, we found that eosinophil responses to IL-1 differed among the populations. These results suggest that eosinophil subpopulations respond selectively to each form of IL-1.