The invention relates to a process for the preparation of a diagnostic X-ray composition. The composition comprises a non-ionic X-ray contrast agent in a pharmaceutically acceptable carrier. More particularly, the invention relates to a process for secondary production of X-ray compositions comprising X-ray contrast agents with a high dissolution temperature. When using the process of the invention,precipitation is avoided and degradation of the contrast agent is reduced. The process of the invention includes heat treatment of iodinated X-ray contrast agents at low pH.
