Abstract: A method of preventing or reducing fluid and electrolyte losses in mammalian subjects under the effect of a stimulus that directly or indirectly causes such losses, by administering a therapeutically effective amount of D-histidine, L-histidine, a racemic mixture thereof, a non-racemic mixture thereof, and pharmaceutically acceptable salts in conjunction with a carrier. In one embodiment the method is useful in reducing or preventing intestinal tract fluid secretions, and fluid and electrolyte losses associated with diarrhea arising from a number of causative agents, such as infectious diarrheas and non-infectious diarrheas. Various therapeutic regimes of histidine administration and formulation are embodied. Therapeutic compositions of histidine in combination with other medicaments, e.g., those that produce a diarrheal side-effect, are disclosed as another embodiment.