Microwave heating of intravenous (IV) fluids is a viable alternative to heating by conventional means, such as by blood warmer(s) or an on-site warming oven, for administration to hypothermic patients and trauma victims. Three 1-l bags each of lactated Ringer's solution, normal saline solution, 1/2 normal saline solution, and 5% dextrose in water were packaged in parenteral containers and heated in a microwave oven from room temperature (21 degrees C) to 40-42 degrees C in 3 minutes. Little difference between temperatures of the four solutions was detected at each of five intervals up to two hours after heating for 3 minutes. Samples were taken before and after heating to assess any potential alterations in sodium, potassium, chloride, calcium, glucose, and lactate levels; differences were within the range of variation of the methods used. Though the plasticizer in the polyvinyl chloride containers is stable to microwave heating, data on other components is incomplete.