Out of 14 cases of poisoning assumed to be due to dextropropoxyphene-containing drugs, propoxyphene and its main metabolite norpropoxyphene could be demonstrated in 11. The concentrations of the drugs were determined shortly after admission and then after 2, 4, 6 and 10 hours (in four cases also after 16 hours). The highest plasma concentration of propoxyphene, 0.74 mug/ml, was found in one case of fatal poisoning. Another patient with a plasma concentration of 0.51 mug/ml showed signs of severe respiratory depression but survived after respirator therapy. In the patients with lower plasma concentrations the poisoning had a benign course. In most cases the plasma concentration of norpropoxyphene exceeded that of propoxyphene even in the first blood sample.