AbstractThe condensation products of rhodanine, 3‐ethylrhodanine and 3‐phenyl‐rhodanine with various polycyclic aromatic aldehydes have been prepared with a view to obtaining compounds with increased bacterial and fungicidal properties. The aldehydes were chosen to yield products of similar skeletal configuration to the less accessible alkyl substituted compounds. It is known that substituted benzylidene‐rhodanine derivatives show increased bacterial activity and the products obtained, by virtue of their structure, should show activity similar to di‐ and tetra‐alkyl substituted derivatives. Condensations were carried out in both ammoniacal and acid media and crystalline coloured condensation products were obtained in