Rehydration is vital to restore the fluids and salts lost during diarrhoea and to prevent dehydration from becoming more severe and possibly fatal. A single solution, administered by mouth and known as Oral Rehydration Salts (ORS) solution, is now available for the treatment of dehydration due to diarrhoea, whatever its cause, in all ,age groups, including neonates. The ingredients in ORS solution are shown here, in grams and in millimoles per litre of drinking water. Only patients with severe dehydration need first to receive intravenous solutions administered rapidly; ORS can then be given as soon as the pulse is strong and blood pressure normal.