To evaluate the safety and efficacy of gadodiamide injection, a nonionic gadolinium chelate complex, in magnetic resonance (MR) imaging of the head and spine, a phase II-III trial was conducted in 439 patients with known or suspected lesions in the central nervous system. All patients received gadodiamide injection in a dosage of 0.1 mmol/kg and were monitored; MR images were evaluated for contrast material enhancement. No serious adverse events or clinically important trends in vital signs, laboratory values, or neurologic status were observed. Gadodiamide injection enhanced or facilitated the visualization of lesions in 266 or 353 patients (75.4%) in whom lesions were shown on unenhanced images, enhanced images, or both; in these 266 patients, the diagnosis was changed in 76 patients (28.6%) and facilitated in 190 patients (71.4%). It is concluded that gadodiamide injection is safe and effective for MR imaging of the head and spine in patients with suspected abnormalities of the central nervous system.