Theophylline total body clearance was calculated in 59 adult patients requiring intravenous aminophylline therapy. Group 1 consisted of 36 chronic obstructive pulmonary disease patients who were cigarette smokers without other conditions known to alter theophylline kinetics (age range: 22 to 79 years). Group 2 consisted of 23 chronic obstructive pulmonary disease patients who were cigarette smokers with a similar degree of congestive heart failure, but free of other characteristics or diseases that affect theophylline disposition (age range: 41 to 81 years). When individual theophylline total body clearance values were plotted against age in each group, poor correlation coefficients were found, indicating that age is not a good predictor of total body clearance of theophylline (group 1: r = 0.101; group 2: r = 0.276). Each group was also broken into 'younger' and 'older' patients. No significant differences in theophylline total body clearance values were found between the younger and older patients for either group I or 2, suggesting that a theophylline dosage reduction is not necessary in cigarette smoking patients over an arbitrary age limit.