The topical effect of the histamine H1-receptor antagonist dimethindene maleate on the wealing response to intradermal histamine, compound 48/80 and house dust mite antigen was studied in 16 subjects using a double-blind procedure. The mean reduction in weal area +/- s.e. mean was 44% +/- 13%, 43% +/- 13% and 31% +/- 13% for histamine, 48/80 and antigen respectively. We conclude that dimethindene maleate is a moderately potent H1-receptor antagonist, and that the inhibition of the 48/80 and house dust mite induced weals is accounted for by the antihistaminic effect of dimethindene maleate.