AbstractThe condensation products of rhodanine, 3‐ethylrhodanine, 3‐phenylrhodanine, 3‐allylrhodanine and 3‐carboxymethylrhodanine with various substituted and unsubstituted pyridine and quinoline aldehydes have been prepared for bacterial and fungicidal evaluation. An earlier series of unsubstituted pyridylmethylene‐rhodanines has thus been extended to include products substituted in either or both of the heterocyclic rings. Such substitution may enhance the already known fungicidal character of such rhodanine‐aldehyde condensation products. The products obtained by the condensation of the quinoline aldehydes may be considered as substituted in a similar manner as the less accessible dialkylpyridine products and it is possible that these two types of compounds will show a similarity in biological activity. Condensations between the rhodanines and the aldehydes were carried out in acid medium and crystalline coloured condensation products were obtained in