In order to study the elimination of Ro 10-1670 (acitretin) and Ro 13-7652, its 13-cis-isomeric metabolite after chronic administration, determination of the residual plasma concentrations of these two compounds were assayed in 9 patients in a range of 22–30 days following cessation of a 2- to 7.5-month course with daily oral doses of 10–50 mg of acitretin. A highly sensitive HPLC method was used (2 ng/ml). Residual plasma concentrations of Ro 10-1670 were below the quantification limit in all cases. Residual plasma concentrations of Ro 13-7652 were below the quantification limit in 7 cases and respectively of 3 and 4 ng/ml in the other 2 cases. These data appear to confirm the absence of storage of acitretin even after an extended course of ther