As a consequence of the widespread industrial and agricultural applications of organotin compounds, contamination of various ecosystems has occurred in recent decades. Understanding how these compounds interact with cellular membranes is essential in assessing the risks of organotin pollution. The organotins, tributyltin (TBT) and trimethyltin (TMT) and inorganic tin, Sn(IV), were investigated for their physical interactions with non-metabolising cells and protoplasts of the yeast, Candida maltosa, an organism that is often associated with contaminated environments. Sn(IV) and TBT uptake occurred by different mechanisms. TBT uptake resulted in cell death and extensive K+ leakage, while Sn(IV) uptake had no effect. TMT did not interact with cells. Of the three compounds, TBT alone altered the membrane fluidity of cells, as measured by the fluorescence anisotropy of 1,6 -diphenyl-1,3,5 -hexatriene incorporated into cells. To further examine the contribution of lipophilic interactions, the influence of pH and NaCl concentration on TBT and triphenyltin (TPT) uptake and toxicity was assessed. Solution pH and ionic composition influence the chemical speciation and toxicity of organotins in the aquatic environment. Organotin compounds may exist as both hydrated cationic species and neutral hydroxides in solution, with the formation of chloride species in the presence of NaCl. The uptake and toxicity of TBT and TPT by C. maltosa was investigated between pH 3.5 and 7.5 and in concentrations of up to 500 mM NaCl. A theoretical model was used to predict the speciation and overall octanolwater distribution ratios (Dow)- TBT and TPT toxicity was correlated with Dow values, corresponding to increasing pH and NaCl concentration and implicating compound lipophilicity as a toxicity determinant.