Novel antiviral (including antiretroviral) compounds are mono- or dicarboxylic acid esters of hypericin in which one or both of the methyl groups of hypericin are substituted by carboxylic acid ester groups of the formula COOR3 in which R3 is alkyl, the chain of which is optionally interrupted by one or more oxygen or sulphur atoms. R3 is preferably methyl, ethyl, propyl, butyl, 2-methoxyethyl or 2-(2-methoxyethoxy)ethyl. The compounds may be formulated into pharmaceutical compositions and may be used in any manner which has previously been known for hypericin.