The effect of the steroidal glycoalkaloid α-tomatine on efflux of cell material from disks of beetroot, potato, apple, and carrot has been investigated. A concentration of 1 mM tomatine caused large increases in efflux from all tissues but 10 μM had no effect. Leakage from potato and apple, but not from beetroot and carrot, was stimulated by 100 μM. tomatine, although losses were smaller. Alkaloid-induced efflux of cell material was reduced considerably by addition of 1 mM CaCl2 and to a lesser extent by 1 mM MgCl2. Cholesterol and its acetate did not reduce leakage from beetroot but higher concentrations of the former caused small reductions in loss of material from potato. The significance of these findings in relation to the action of other membrane-active compounds is discussed.