This chapter describes technetium complexes which fulfil the basic requirement to cross the blood brain barrier, and includes those complexes which, by design or luck, are retained for sufficient time for single photon emission computerised tomography (SPECT) imaging. Developments in positron emission tomography in the late 1970's and iodine-123 radiopharmaceuticals for SPECT in the early 1980's greatly enhanced the general appreciation for the potential of cerebral perfusion imaging in the diagnosis and management of cerebral vascular disease and other neurological disorders. In order to provide an image of cerebral perfusion, a radioactive tracer must, following intravenous administration, be extracted from the blood stream into cerebral tissue. This extraction process should proceed with high efficiency, and result in a regional distribution of tracer which reflects regional blood flow. Studies involving the application of technetium complexes of oxines are summarized.