Cyclosporin is known to cause a decrease in renal blood flow and glomerular filtration rate in both humans and animals. These acute modifications are reversible if the drug is withdrawn, and seem to be caused by a local hormonal imbalance between vasoconstricting and vasodilating substances. We studied human glomeruli incubated with either CsA alone, iloprost alone, or CsA + iloprost. Photomicrographs of glomeruli were taken at t0, t1, t2 and t5 min and glomerular areas were measured with a videoanalyser linked to a computer. Results show a significant vasoconstriction with CsA alone, and no significant modification of glomerular areas with iloprost or CsA + iloprost. We conclude that iloprost prevents CsA-induced vasoconstriction in human glomeruli in vitro.