Spa treatment at the Dead Sea has been shown to help psoriasis for many thousands of patients over the years. It is not known, however, what aspect of the treatment produces benefit. In this double-blind randomized study, Dead Sea salts (DSS) made up as a 30% lotion were used to treat patients with plaque psoriasis and compared with the base lotion as placebo. There were 12 patients in each group, and PASI scores were measured at 0, 4, 8 and 12 weeks. There were five withdrawals (one placebo and four DSS lotion). Analysis of PASI scores on those who completed the study showed slight improvement with the placebo and no change with the DSS lotion. Thus in this study 30% DSS lotion was not shown to have any beneficial effect.