The influence of 3-9 months of combined low dose oral contraceptives on theophylline pharmacokinetics was studied in 10 adolescent females (age 15-18 years, mean +/- SD 17 +/- 1) and compared to 10 age-matched control subjects (age 13.8-19 years, mean +/- SD 16.5 +/- 1.6). The distribution volume (0.44 +/- 0.06 L/kg in control vs. 0.44 +/- 0.09 L/kg oral contraceptive group), total body clearance (0.78 +/- 0.13 ml/kg/min vs 0.78 +/- 0.18 ml/kg/min) and elimination T 1/2 (402 +/- 78 min vs. 409 +/- 126 min) were identical in the two groups. It appears that during the first 3-9 months of low dose oral contraceptive treatment, these steroids do not alter the pharmacokinetic behaviour of theophylline in adolescent females.