A process for producing solid solutions in powder or granule form of slightly soluble substances in which the slightly soluble substance is in the form of a molecular dispersion in an excipient matrix, by atomizing a solution of the active ingredient and of the matrix excipients, which comprises heating an aqueous suspension of the slightly soluble substance in the presence of the matrix excipients to temperatures above the boiling point under atmospheric pressure, and dissolving the slightly soluble substance, and subsequently converting the solution of the slightly soluble substance and of the matrix excipients by atomizing and drying into a solid form, where the temperature of the spray solution before feeding into the atomizing apparatus is 90.degree. C. to 350.degree. C.