As part of a phase III clinical trial, 25 patients with suspected intracranial or spinal disease underwent magnetic resonance (MR) imaging before and after intravenous injection of 0.1 mmol/kg Gd-HP-DO3A (1,4,7-tris[carboxymethyl]-10-[2' hydroxypropyl]-1,4,7,10- tetraazacyclododecane), a neutral (nonionic) gadolinium chelate. Laboratory analysis included a complete blood count; blood chemistry; measurement of electrolyte levels; hepatic function, clotting function, and iron metabolism panels; and urinalysis both before and 24 hours after contrast agent administration. No statistically significant changes related to contrast agent administration were noted in laboratory values after administration of the contrast agent. In this selected group of patients, the contrast agent-enhanced study provided greater diagnostic information than did the precontrast study in 69% of head cases and 67% of spine cases. These initial clinical trials demonstrate that Gd-HP-DO3A is a safe, efficacious agent for head and spine examinations.