Hydrophobic contaminants (e.g., O-alkylated derivs.) and residual org. solvents are removed from the X-ray contrast agent iohexol by the use of a solvent such as ethanol which the iohexol is insol. one procedure, ethanol is added to aq. soln. of iohexol. another procedure, the iohexol is suspended ethanol and then allowed to crystallize. Cryst. iohexol having a residual solvent content <100 ppm is prepd. this way.