Abstract The effects of trialkyltin compounds on the colchicine‐binding activity and the in vitro polymerisation of rat brain tubulin have been investigated. Trialkyltins at concentrations between 10 and 100 μM inhibited the colchicine‐binding activity of purified tubulin preparations derived from rat brain. Viscometric studies have shown that the same concentrations of trialkyltins also inhibited the in vitro polymerisation of tubulin. Both the effects were found to be concentration dependent. However, trialkyltins did not interfere with the in vitro preassembled microtubules. The reasons which are believed to explain the inhibitory effects of these compounds are discussed.