Non-compliance to dosage regimes is an important clinical problem with severe repercussions for the management of chronic illnesses requiring continued treatment. In the present study, we evaluated the degree of non-compliance in a group of 100 patients with chronic asthma undergoing continued treatment with theophylline, and the effect of the application of a monitoring programme on their degree of compliance. The evaluation was carried out by anamnesis and from the level/dose ratio. In the control group studied (n = 50) the degree of non-compliance was 44% and in the previously monitored group (n = 50) it was 18%. Serum theophylline levels in the former were: 7.6 +/- 5.8 micrograms/ml, significantly lower (P less than 0.005) than that observed in the latter: 10.1 +/- 4.0 micrograms/ml. The use of monitoring programmes can improve the degree of compliance.