METHODS: 45 women with pre-eclampsia were randomized to receive either L-arginine or placebo until day 10 post-partum. Primary outcome measures including MAP, glomerular filtration rate and proteinuria were assessed on the third and tenth days postpartum by inulin clearance and albumin-to-creatinine (A/C) ratio. NO, cyclic guanosine 3'5' monophosphate (cGMP), endothelin-1 (ET) and asymmetric-dimethyl-arginine (ADMA) and arginine levels were assayed prior to delivery, on the third and tenth day postpartum. Healthy gravid women provided control values. Assuming a standard deviation of 10 mmHg, the study was powered to detect a 10 mmHg difference in MAP (alpha 0.05, beta 0.20) between the study groups.