A benzonaphthalene compound has the formula ##STR1## wherein R.sub.1 represents ##STR2## or (ii) --CH.sub.2 OH; R.sub.6 represents ##STR3## or OR.sub.7 wherein R.sub.7 represents hydrogen, alkyl having 1-20 carbon atoms, monohydroxyalkyl or polyhydroxyalkyl, r' or r" represent hydrogen, lower alkyl, mono or polyhydroxyalkyl, aryl or a residue of an amino acid or a sugar, or together form a heterocycle; R.sub.2 represents hydrogen, alkyl having 1-15 carbon atoms, alkoxy having 1-4 carbon atoms or a cycloaliphatic radical; R.sub.3 represents hydrogen, hydroxy, alkyl having 1-4 carbon atoms, alkoxy having 1-10 carbon atoms, a cycloaliphatic radical, a thiocycloaliphatic radical or --O--Si(CH.sub.3).sub.2 --R.sub.8 wherein R.sub.8 represents lower alkyl; and R.sub.4 and R.sub.5 represent hydrogen, lower alkyl, hydroxy or lower acyloxy.This compound is useful in the topical and systemic treatment of dermatologic diseases and in the treatment of the degeneration of conjunctive tissues. The compound also possesses anti-tumor acitivity.