In the course of six months, the influence of the oral depot contraceptive, Deposiston (3 mg ethinylestradiol sulphonate and 10 mg norethisterone acetate per menstrual cycle) on the pharmacokinetics of caffeine as a model substance was studied in seven women in intraindividual comparison. The first examination began prior to administration of Deposition. The women were subjected to little challenge as saliva was used as the measuring compartment. Deposiston was found markedly delay the elimination half-life life of caffeine (p less than 0.05): t1/2 prior to therapy 4.9 +/- 2.6 h and, after as little as 2 mg ethinylestradiol sulphonate 8.0 +/- 3.5 h. In contrast to the effect observed for preparations containing less estrogen, these longer half-lives persisted throughout the trial. As expected, the AUC values were slightly elevated during this period, whereas clearance values were reduced.