PATIENTS suffering from psoriasis frequently have a low serum folate (Knowles, Shuster and Wells, 1969; Shuster, Marks and Chanarin, 1967). It is usually accepted that this is due to loss of folate in the psoriatic desquamation (Hild, 1969), though it has been suggested that increased utilisation of folate is possibly a more important factor (Touraine, Revuz, Zittoun, Jarret and Tulliez, 1973)....