Urinary total morphine: total codeine ratios were studied in two groups of people. Group A consisted of 76 subjects receiving three different medicinal preparations containing morphine or codeine, while Group B consisted of 33 drug abusers detected at urinary mass screening. Distinct differences in these ratios were observed. In Group A, total morphine: codeine ratios of 1:2.6 and below were obtained for subjects consuming either Tablet Codeine Co or Syrup Phensedyl. Subjects consuming Kaolin et Morphine mixture did not excrete any codeine in the urine. In Group B, total morphine: total codeine ratios of 1.9:1 and above were obtained. In addition all subjects in Group B excreted both morphine and codeine. The clear separation of the morphine: codeine ratios makes this a possible index to differentiate between these groups.