In the investigations of Krebs and Schaltegger between 1964 and 1972 on the structure specificity of the antipsoriatic anthrones it could be shown that at least a 1-hydroxy-9-anthrone is necessary for their efficacy. This structure was then called "minimum structure of the antipsoriatic anthrones'. Since even very minor changes of this structure in most cases lead to inactive compounds, only a few antipsoriatic anthrones have been found so far. Their most important representative chrysarobin, anthralin and I-hydroxy-9-anthrone have been known for more than 60 years. The later discovered antipsoriatic anthralin derivatives, triacetoxy-anthracene and 10-acyl-anthralin, are probably hydrolysed in the skin and thus act as their parent compound anthralin. The strong structure-activity dependence of the antipsoriatic anthrones seems to include a highly specific and complex mechanism of action.