This review summarizes the biological profile of the nonionic contrast medium, iohexol, with particular emphasis on neurovascular and myelography applications. Iohexol was compared with conventional ionic media and with newer nonionic agents in a variety of animal models. Studies of systemic toxicity (teratogenicity, mutagenicity, and embryotoxicity effects) and cerebrovascular effects (epileptogenicity and arachnoiditis potential) are reported. Results indicate that iohexol has a lower toxicity than ionic and other nonionic contrast media.