OBJECTIVE: WHO recommends Ringers lactate (RL) and Normal Saline (NS) for rapid intravenous rehydration in childhood diarrhea and severe dehydration. We compared these two fluids for improvement in pH over baseline during rapid intravenous rehydration in children with acute diarrhea. DESIGN: Double-blind randomized controlled trial. SETTING: Pediatric emergency facilities at a tertiary-care referral hospital. INTERVENTION: Children with acute diarrhea and severe dehydration received either RL (RL-group) or NS (NS-group), 100 mL/kg over three or six hours. Children were reassessed after three or six hours. Rapid rehydration was repeated if severe dehydration persisted. Blood gas was done at baseline and repeated after signs of severe dehydration disappeared. OUTCOME MEASURES: Primary outcome was change in pH from baseline. Secondary outcomes included changes in serum electrolytes, bicarbonate levels, and base deficit from baseline; mortality, duration of hospital stay, and fluids requirement. RESULTS: Twenty two children, 11 each were randomized to the two study groups. At primary end point (disappearance of signs of severe dehydration), the improvement in pH from baseline was not significant in RL-group [from 7.17 (0.11) to 7.28 (0.09)] as compared to NS-group [7.09 (0.11) to 7.21 (0.09)], P=0.17 (after adjusting for baseline serum Na/ Cl). Among this limited sample size, children in RL group required less fluids [median 310 versus 530 mL/kg, P=0.01] and had shorter median hospital stay [38 versus 51 hours, P=0.03]. CONCLUSION: There was no difference in improvement in pH over baseline between RL and NS among children with acute diarrhea and severe dehydration.