The purpose of this open, noncomparative study with acitretin (Ro 10-1670) was to evaluate the clinical response of patients with various nonpsoriatic disorders of keratinization and to establish for these patients the optimal dosage for both efficacy and tolerance. Thirty-three patients (21 adults and 12 children or adolescents) with ichthyoses, palmoplantar hyperkeratosis, or Darier's disease were treated for a period of 4 months. Most patients showed marked improvement or remission. The results obtained in congenital ichthyosiform erythroderma, lamellar ichthyosis, and Papillon-Lefèvre syndrome were judged as better than those usually reported with etretinate. The side effects observed in our patients were similar to those reported with etretinate, with the exception of scaling of palms and soles, which had an incidence and severity greater than expected with etretinate. The optimal acitretin dosage providing the best efficacy with minimal undesirable effects varied from patient to patient. The mean daily dose (±SD) was 27 ± 11 mg in adults and 0.7 ± 0.2 mg/kg in children or adolescents.