Twenty four of 30 patients with chronic plaque psoriasis completed a double-blind randomized paired comparison of dithranol in Lassar's paste versus dithranol and fluocinonide in Lassar's paste. There was a more rapid reduction in severity of the psoriasis on the side treated with the dithranol and fluocinonide mixture, but no difference in the final time to clearance between the two sides. There were fewer burning episodes on the side treated with dithranol and fluocinonide and greater staining of the skin. Of the 20 patients who were subsequently followed up for up to 3 months, 11 had relapsed more on the side treated with dithranol and fluocinonide, two on the side treated with dithranol alone and in seven there was no appreciable difference. It was concluded that the addition of a topical steroid to a conventional dithranol regimen produced more rapid initial clearance and less burning, but more rapid relapse of the psoriasis.