To determine the usefulness of cerebral blood flow imaging for the diagnosis of brain death, 4 female and 12 male patients, aged 19 to 69 years and suffering from various intracranial lesions, were studied. In addition to neurologic examination, electroencephalographic recording, and cerebral angiography, tomographic brain scintigraphy was performed using a SPECT system with a LEAP collimator after the intravenous administration of 555 MBq Tc-99m HMPAO. The radioisotopic scanning procedure revealed no intracranial perfusion in 14 of the 16 patients. Only minimal cerebellar blood flow was seen in one patient. In another, residual right-sided supraten-torial flow was initially present but.absent in a follow-up HMPAO SPECT. Carotid angiography (four-vessel contrast media angiography) confirmed the above results without exception. Because HMPAO is taken up by normal brain tissue with no significant redistribution for several hours, the tracer is particularly helpful in cases of suspected brain death. The quality of the tracer must be established by chromatography. Interpretation of the SPECT images produces reliable and reproducible results. In conclusion, cerebral blood flow imaging with HMPAO is a safe, noninvasive procedure for the determination of brain death, that produces fast, reliable, reproducible, and easy-to-interpret results.