In this study investigations were carried out on pharmacokinetics of buprenorphine after it had been applied subcutaneously. Up to now no pharmacokinetic data exist using this kind of application with relevant clinical doses. METHODS With 6 patients, who had major general surgery under balanced anaesthesia, buprenorphine was given in a single subcutaneous injection of 5 micrograms/kg bodyweight for postoperative pain relief. Over a period of 48 hours the level of buprenorphine in blood plasma was measured. The analyses were done with a modified HPLC method with electrochemical detection which is able to achieve measurements as low as 40 pg/ml of plasma. The pharmacokinetic values were calculated with the "Topfit" pharmacokinetic computerised programme. RESULTS Whereas the period of time (tmax) to reach peak plasma concentration (Cmax) after subcutaneous application is much longer than with other parenteral application forms, the plasma concentration levels tend to be similar after 20 minutes. The most important finding of this study is that the mean terminal half-life (t1/2c) of buprenorphine is 23 hours. However, the presently available data for other application forms in respect to terminal half-life did not produce the same results. This can be explained by the use of insufficiently sensitive analytical procedures and by too short periods of observation of 3 and 13 hours respectively, leading to values of t1/2c of 2 and 5 hours. CONCLUSIONS These results indicate that the terminal half-life (t1/2c) of buprenorphine is much longer than had been supposed. It confirms clinical findings of sufficient pain relief by showing measurable uptake of buprenorphine after subcutaneous application.