A process for the prodn. of iohexol comprises alkylating 5-acetamido-N,N'-bis(2,3-dihydroxypropyl)-2,4,6-triiodoisophthalamide with 1-chloro-2,3-propanediol using 2-(2-methoxyethoxy)ethanol as the reaction solvent the presence of a base (e.g., sodium hydroxide).