An earlier study done by the National Swedish Association for Penal Reform found disturbingly high levels of prescriptions for tranquillizers and sedatives were being used in certain prisons. The current study examined medicine use in four prisons -- two with the highest medicine use in the earlier study and two with the lowest use. Since the medicine forms generally used do not lend themselves to easy analyses of the medicine prescribed for each patient, the period of use, or the dosages, a new form was devised for the study. This change in forms prevented a historical study of medicine use. The study was therefore designed as a prospective study, and the prison staffs knew that prescribing practices would be observed from January 1 through August 31, 1981. Two independent methods were used to determine medicine use. One method determined the medicine used on the basis of store quantities at the beginning, middle, and end of the period, together with the deliveries made; and the second method determined use through the individual prescriptions recorded on the patient medicine forms. The principal finding was that for medicine classified as narcotic drugs, use was 90 percent lower than the levels reported in the earlier study. Such a significant difference in findings was probably due to the staff's knowledge that prescription practices were being observed in the second study. The first method for determining medicine use was found to be a reliable and simple monitoring technique. The medicine form used in the study is provided. Tabular data are included.