The technique of micropipette aspiration of individual erythrocytes has been used to determine the critical tension (Ter) for lysis of hypotonically slightly swollen normal erythrocytes and erythrocytes exposed to the influence of lipid-soluble chemical compounds. The value of Ter of preswollen normal erythrocytes was 12.23 ± 1.84 dyn/cm (1 dyn = 10 μN), a value which agrees well with that found by other workers. The Ter was increased in normal erythrocytes following exposure to four aliphatic alcohols, chloroform, and phenol. The optimal concentration resulting in 24–33% increase in Ter for the six compounds studied was very similar to the concentration previously found to be optimal in conferring increased resistance to osmotic hemolysis.The determination of Ter by micropipette aspiration of individual erythrocytes enables a range of concentrations of lipid-soluble compounds to be studied and led to the demonstration of a biphasic effect of the alcohols on the surface area elastic modulus.The studies now reported confirm the findings of Seeman (SEEMAN, P. 1972. The membrane action of anesthetics and tranquilizers. Pharmacol. Rev. 24(4), 583.) and suggest that incorporation of relatively short chain alcohols is concentration dependent and is associated with alterations in the mechanical-rheological properties of the membrane in a manner which appears analogous to the previously published reports on effects of alcohols on membrane transport and enzymatic activity. These findings suggest that lipid-soluble compounds at optimal concentrations influence both material properties and membrane-related functions, presumptively due to alterations in lipid–lipid, and (or) lipid–protein interactions.