Tohoku University has nearly a 30-year-long history of basic and clinical research in molecular imaging using radiopharmaceuticals. This article briefly overviews the various achievements of Tohoku University in the fields of oncology and neuroscience. It is noteworthy that most of the early data regarding oncology diagnosis using positron emission tomography (PET) were produced at the Cyclotron and Radioisotope Center of the university. Also, the center has various academic contributions to the filed of neuroscience. One of its major contributions is molecular imaging of histamine H1 receptors, and recent achievements in this topic are summarized in this paper. The histaminergic neuronal system is associated with various functions such as wakefulness, the sleep-wake cycle, appetite control, learning, memory and emotion. Using [11C]doxepin and PET, various studies have been conducted regarding physiological changes such as aging and pathological changes such as Alzheimers disease, depression, and schizophrenia. In addition, histamine H1 receptor antagonists (antihistamines) are frequently used for the treatment of allergic disorders. These compounds can induce sedative side effects that can cause serious traffic accidents. Objective measurement of the sedative property of antihistamines was started in the early 1980s and was established at Tohoku University using H1 receptor occupancy as an index. In the future, PET will undoubtedly be used more frequently in drug development.