The influence of various test meals, and of fluid volumes, on the bioavailability of theophylline from asolid dosage form has been studied in healthy male volunteers. Absorption of drug was faster after dosing immediately following a high protein meal than after a high fat or a high carbohydrate meal. Absorption from a solution was faster than from asolid dosage form in all treatments; areas under serum level time curves after dosing were also significantly higher up to 12 hr. Areas up to 12 hr after dosing also tended to be higher after the high protein meal and after dosing with 500 ml water on an empty stomach than after other solid dose treatments.