In order to assess the adequacy of digitalis therapy in Finland we studied its practice and control in 747 patients who were receiving it regularly. The patients were derived from a sample (n = 8000) representative of the adult Finnish population. More than 90% of the patients were receiving digoxin, mostly 125 micrograms or 250 micrograms, once daily. Few patients were taking digitalis as the sole drug prescribed. The mean number of prescribed drugs for each patient (including digitalis) was 4.2 for men and 4.6 for women. 85% of the patients generally visited their "own" doctor. About 90% of the patients had seen a doctor at least once during the previous 12 months. In spite of this, the control of the therapy was generally considered poor, since almost half the patients were uncertain when the next visit to the doctor would be. Inadequately low serum digitalis concentrations, suggesting inadequate or questionable use of the drug, were observed in 30% of the patients. In 15% of the patients the therapy was considered especially questionable. Probably due to variable prescribing habits in general practice, the proportions of patients on poorly controlled, inadequate or questionable digitalis therapy varied remarkably between regions within the country. The results suggest that digitalis therapy in Finland is often inappropriate. We conclude that the practice and control of digitalis therapy need careful reappraisal in this country.