Acute renal failure and veno-occlusive disease of the liver are serious complications following stem cell transplantation (SCT) and contribute to the non-relapse mortality associated with this procedure. Endothelins, a family of vasoconstrictor peptides, may be involved in the pathogenesis of a variety of renal and hepatic diseases, including CsA-associated hypertension and the hepatorenal syndrome. In order to study the relevance of endothelins to SCT-related liver and kidney dysfunction, we determined endothelin-1 (ET-1) levels in plasma samples obtained from 65 patients (38 autologous, 27 allogeneic) 7 days before and 7, 14 and 28 days after SCT. A steady increase in plasma ET-1 was observed after SCT (5.36 pg/ml, 95% CI 4.30-6.43 on day +28 vs 3.82 pg/ml, 95% CI 3.21-4.43 on day -7; P = 0.020). No differences in ET-1 levels existed between autologous and allogeneic SCT recipients at any of the time points studied (P = 0.561). In addition, no significant differences were observed among patients with renal dysfunction vs those without (P = 0.187), nor in patient groups with or without hepatic dysfunction (P = 0.075). In conclusion, even though plasma ET-1 levels showed a steady increase following SCT, no correlation could be found with development of SCT-related kidney or liver dysfunction.