Abstract: The invention relates to novel pharmaceutical compositions which are effective against a wide spectrum of viruses belonging to the Retroviridae family. The active ingredient of the compositions is a thiosemicarbazone compound as herein defined. The compounds are similar to the well-known compound M-IBT (methyl isatin-.beta.-thiosemicarbazone) which has been widely used against smallpox. Contrary to the compounds used according to the present invention, one of which is novel by itself, M-IBT is not effective against viruses of the Retroviridae against which the novel compositions are active.