Five patients suffering from lamellar ichthyosis and 3 from epidermolytic hyperkeratosis (previously called non-bullous and bullous congenital ichthyosiform erythroderma) were treated from 11 to 52 months with the synthetic aromatic retinoid Tigason (RO 10-9359). In all cases of lamellar ichthyosis the results were judged as good to excellent, while none of the patients with epidermolytic hyperkeratosis gave more than a slight response. The reason for the poorer results in the latter condition was that effective therapeutic dosages in relation to ichthyosis invariably produced increased blistering. These and other side effects such as cheilitis, mild dryness of mucous membranes, slight hair loss, and pruritus, in no case necessitated discontinuation of the drug.