The benzo-pyrones (including coumarin) are a very effective therapy for mild thermal oedema and cases of acute and chronic lymphoedema. In this preliminary report the distribution of a single injected dose of coumarin was followed in normal tissues of rats for 100 hours. Comparisons are to be made later with drug levels in thermally injured and lymphoedematous tissues. The resluts show 7-4% of the injected dose to remain in the tissues after 100 h. During this time 30-9% was excreted in the faeces and approximately 47% excreted in the urine. At any given time most of the dose was present in the gut, muscular tissues, skin and liver. For the gut tissues this was 33%, for the muscular tissues 28%, for the skin 18% and for the liver 16%. The highest concentrations per gram of tissue were however in the kidney and liver, representing the two organs of metabolism and excretion of the coumarin.