HL-A typing was performed on 97 patients with pustular psoriasis. HLA-B27 was found increased for the combined three subgroups: localized psoriasis of palms and soles, acrodermatitis continua and generalized pustular psoriasis, who were associated with a high incidence of arthritis. These subgroups have this in common with Reiter’s disease indicating a link between the entities. In persistent palmo-plantar pustulosis an increased incidence of HLA-Bw35 was found. HLA-B13, HLA-B17 and HLA-Bw37 which are found markedly increased in psoriasis vulgaris were in acrodermatitis continua, generalized pustular psoriasis and persistent palmo-plantar pustulosis either absent or not increased as compared with the control population. 7 of 30 patients with localized psoriasis of palms and soles had one of these antigens. Our findings confirm that psoriasis vulgaris and pustular psoriasis as such, seem to be different aetiological entities. Some patients with localized psoriasis of palms and soles may be true psoriatics which besides their psoriasis have a tendency to develop a pustular reaction in their palms and soles similar to persistent palmo-plantar pustulosi