AbstractAntifungal test results are given for a number of functionally substituted organo‐tin compounds.Among such compounds of the type R4Sn, only one, cyanomethyltri‐n‐butyltin, exhibits appreciable fungitoxicity. Activity in this case is explained by the instability of the cyanomethyl‐tin bond to hydrolysis.The results obtained with compounds of the type R3SnX show that the introduction of functional substituents in general reduces antifungal activity. This is most pronounced in the case of water‐solubilising sub