1 Serum theophylline levels were performed in 26 patients with chronic lung disease receiving rapid release theophylline (125 mg 6 hourly) and 28 patients receiving slow release theophylline (250 mg 12 hourly) under steady state conditions. 2 For rapid release theophylline the mean + s.d. serum theophylline levels at 0 and 2 h were 41.0 + 21.7 and 52.3 + 20.9 mol P1-respectively and for slow release theophylline at 0, 4 and 6 h 43.7 + 25.5, 50.9 + 23.0 and 51.7 + 26.4 pmol I1 respectively. 3 Serum theophylline monitoring with slow release theophylline was performed in 70 patients with chronic lung disease. The initial dose was 250 mg administered 12 hourly. 4 The mean + s.d. steady state serum theophylline level achieved was 76.0 + 18.8 jimol -1 and the mean + s.d. dose to produce this level was 9.4 + 2.3 mg kg-' day-'. There was no correlation between dosage and serum theophylline level. 5 Sixty percent of patients required a dosage change for stabilization (375 to 1000 mg/day). Seventeen patients reported unwanted effects (nausea or tremor), which either settled quickly or resolved with dosage reduction. 6 Serum theophylline levels were obtained at different dosages in 44 patients and 18 patients demonstrated dose-dependent kinetics. 7 An initial dose of 500 mg/day is recommended and dosage increments should not exceed 125 mg/day with monitoring by serum theophylline levels.

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