Endothelin-1 (ET-1) was measured after extraction from plasma of normal adults (5.9 +/- 1.9 pg/ml, n = 22), normal children (7.1 +/- 1.86 pg/ml, n = 29), non-haemodialysed children with chronic renal failure (CRF) (11.1 +/- 1.8 pg/ml), n = 10), renal graft recipients (9.5 +/- 3.4 pg/ml, n = 37), haemodialysed children 24 h after a haemodialysis session (20.02 +/- 10.9 pg/ml, n = 26) and haemodialysed children before and after a haemodialysis session (15.31 +/- 10.6 and 13.8 +/- 8.5 respectively, n = 14). A sensitive and specific radioimmunoassay was used. ET-1 was significantly higher in non-haemodialysed CRF children and in renal graft recipients than in normal children (P < 0.001 and P < 0.01, respectively) and significantly higher in haemodialysed children when compared with normal children, non-haemodialysed CRF children and renal graft recipients (P < 0.001). ET-1 concentrations were similar in normal children and normal adults. ET-1 was inversely correlated with glomerular filtration rate in non-haemodialysed CRF children (r = -0.39, P < 0.01) and positively correlated with extracellular volume in haemodialysed children (r = 0.435, P < 0.03). After haemodialysis, ET-1 increased in 6 and decreased in 8 of the 14 children studied before and after a haemodialysis session.