A nomogram was evolved for guiding and standardizing i.v. theophylline [a bronchodilator] therapy in hospitalized patients. It provides rapid calculation of a loading dose based on body weight and previous therapy and a maintenance infusion rate related to 3 categories of expected metabolic activity. The guidelines were prospectively used in the treatment of 72 patients, mainly in a respiratory care unit. The nomogram was successfully used to attain near-steady-state serum concentrations in the therapeutic range of 8-20 mg/l in 72% of patients, with only 2 patients outside of the range of 5-25 mg/l. These guidelines facilitate initial theophylline dosage in older patients with liver and cardiac disease and provide a rational basis for interpreting serum concentration measurements and adjustment of drug therapy [to minimize adverse side effects].