This pilot study evaluated the efficacy and side effects of a combination of initial patient-controlled analgesia (PCA) for dose-finding with transdermal fentanyl administration. Twenty inpatients, requiring strong opioids for severe cancer pain, received intravenous fentanyl on an on-demand basis over a 24-h period. The amount of fentanyl administered was then used as a guideline for selecting a suitable transdermal therapeutic system (TTS) on the 2nd day, which remained in place for 3 days. The size of a 2nd TTS, being used from day 5 to 7, was adjusted according to the amount of supplementary intravenous fentanyl doses on day 3. From day 4 to 7 intravenous fentanyl was stopped, and subcutaneous morphine was made available as a rescue medication. A standardized adjuvant medication was allowed. Pain intensity, pain relief, quality of sleep, mood, general state of health, activity, mobility, rescue morphine consumption and side effects were assessed using a diary after baseline pain and symptoms were recorded. Vital functions were monitored and fentanyl plasma levels were measured daily in 15 patients. The use of TTS fentanyl in combination with initial dose titration using PCA gave rapid and statistically significant pain relief. Patient compliance and acceptance were excellent. In the absence of severe side effects the main complaints were dryness of the mouth and constipation. Increasing pain intensity and increasing supplementary morphine requirements as well as decreasing plasma fentanyl levels on day 7 may indicate that conversion ratios from intravenous to transdermal administration should be increased or that TTS should be changed earlier.(ABSTRACT TRUNCATED AT 250 WORDS)