Captopril treatment was given to 30 children aged 8 months to 16 years (mean age 10.1 years) with renal hypertension when combinations of one or more of betablockers, diuretics, clonidine and hydralazine had failed to reduce blood pressure in the majority of the children. Dosages of captopril varied between 0.5 and 11.0 mg/kg BW, which was combined with furosemide in 15 cases, betablockers in three cases, betablockers and clonidine in two cases. Pretreatment mean plasma renin activity (PRA) was 7.9 (0.8-89.4) ng AT/ml/h in 22 of the 30 children and 59% had more than 2.0 ng AT/ml/h. Blood pressure fell from a mean of 158/109 (range 135/75 - 240/140) mm Hg to a mean of 120/76 (range 110/65 - 150/100) mm Hg. Mean duration time was 10.1 months (1-47 months). Skin rash occurred in three cases and taste disturbance in one case. Falling glomerular filtration rate was observed in two children with diseases of the renal vessels. After withdrawal of captopril renal function returned to the pretreatment level. Angiotensin converting enzyme inhibition for treatment of hypertension in childhood has proved to be efficient and safe in these 30 children.