SUMMARY Certain samples of potato tubers have been found to contain an interfering sub stance which is estimated as alcohol by the micro-method of Friedemann and Klass (1936) as modified by Saifi (1940). This non-alcohol material can be removed by washing the alcohol-distillate with purified heptane. Both alcohol and the interfering non-alcohol material were shown to accumu late in potatoes held in nitrogen. In earlier work (Saifi, 1940; Barker and Saifi, 1951) the micro-method of Friedemann and Klass (1936) was modified for use in estimating alcohol in potato tissue. The method finally adopted, for convenience of reference called method A, was as follows. The clearing agents (20 ml. 10 per cent, sodium tungstate and 20 ml. 10 per cent, mercuric sulphate dissolved in 2N sulphuric acid) were added to 20 g. potato tissue, as frozen powder, and the mixture left for 4 to 6 hours at room temperature with occasional shaking. This period allowed equilibrium to be attained between the alcohol content of the tissue and the solution. The alcohol was then distilled from an aliquot of the super natant solution, the alcohol-distillate oxidized with alkaline permanganate, and the residual permanganate titrated with thiosulphate. The final oxidation and titration procedure were as described by Friedemann and Klass. The method is thus not specific ; any volatile substance which is not retained by the clearing agents and which reduces alkaline permanganate would be in cluded in the estimation. The term alcohol as used throughout the note does not, therefore, necessarily signify only ethanol. Method A gave consistent results with the stocks of potatoes tested in 1939 and 1940 and the recovery of ethanol added to the tissue was 98-0;ti-o per cent. Later, however (i.e. in 1950), variable figures for alcohol content were obtained with the potatoes then in use, particularly with samples which had been held in nitrogen for about 25 days at io° C. Moreover, re-distillation from lime and mercuric sulphate, as recommended by Friedemann and Klass for certain tissues, gave a distillate which appeared to contain more alcohol than the original distillate. Passing the distillate before condensation through a trap, containing saturated sodium hydroxide and mercuric chloride (Kozelka and Hine, 1941), gave similar results. This was evidence that, in addition to alcohol, some non-alcohol material was being oxidized by the alkaline per manganate. The problem of removing the interfering material appears to have been Journ. of Experimental Botany, Vol. II, No. 5.