This randomized prospective study measured the effects of an intravenous opioid bolus on cerebrospinal fluid pressure (CSFP), mean arterial pressure (MAP), and cerebral perfusion pressure (CPP) during skull-pin insertion. Twenty-two adult patients scheduled for elective craniotomy for supratentorial lesions were studied. Outcome variables were MAP, heart rate (HR), and lumbar CSFP. The standardized anesthetic regimen included fentanyl (2 microg/kg), thiopental (5-7 mg/kg), lidocaine (1.5 mg/kg), isoflurane (0.3-0.7 minimum alveolar anesthetic concentration), and vecuronium (0.1 mg/kg). During stable anesthesia, sufentanil (0.8 microg/kg) or fentanyl (4.5 microg/kg) was given as a bolus before skull-pin insertion. The hemodynamic effects of the opioid injection were modified with phenylephrine and/or atropine when indicated. CSFP remained unchanged in both treatment groups. MAP and CPP increased approximately 10 mm Hg after skull-pin insertion (P<0.001). In the sufentanil group, HR decreased approximately 10 bpm after opioid injection and remained decreased throughout the study. In fentanyl-treated patients, HR decreased 8 bpm after opioid injection but returned to preopioid rates after skull-pin insertion. In conclusion, in anesthetized patients, an intravenous bolus of fentanyl or sufentanil prior to skull-pin insertion results in stable values of CSFP, CPP, BP, and HR when the hemodynamic effects of the opioid are modified with phenylephrine and atropine.