The effect of low potassium regimes on two lines, ILL 6796 (salt-tolcrant) and ILL 6439 (salt-sensitive), of lentil (Lens culinaris) was studied in a pot experiment under glasshouse conditions. Plants of the two lines were treated with 78, 39, 19.5, and 9.75 mg K·L⁻¹ in Rorison’s nutrient solution. ILL 6796 excelled ILL 6439 in biomass production under varying K regimes. Of the various organic solutes measured in the present study only total soluble sugars proved to be helpful in discriminating the lines, i.e., total sugars increased consistently in ILL 6796 with a decrease in K level of the growth medium, whereas in ILL 6439 they decreased significantly with a decrease in K levels. ILL 6796 showing high efficiency for K utilisation (high shoot growth) could be of great economic value in terms of its use in soils deficient in K.