The method based on the interval algorithm is one of the techniques used to find all direct current operating points of nonlinear circuits. Many approaches have been proposed to enhance the efficiency of the interval method. Amongst them, the linear programming narrowing (LP-narrowing) strategy has been proposed and it shows very promising results. In this paper, a modification of the LP-narrowing technique is proposed. The proposed technique is applied with the interval-based method to find all direct current solutions of a circuit whose nonlinear elements are only diodes and bipolar junction transistors. It employs the voltage-current characteristic of diodes to contract the size of the box under consideration before applying the interval operator. The proposed technique has been implemented by using the C-XSC Toolbox and the GNU Linear Programming Kit package (GLPK). Its performance is evaluated by testing with some nonlinear circuits. The results indicate that the proposed technique can reduce the number of search boxes and improve the computation time. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.