An expression for the potential energy of electrostatic interaction between two soft cylinders (i.e., polyelectrolyte-coated cylindrical particles) in an electrolyte solution is derived by applying Derjaguin's approximation to the corresponding interaction energy between two parallel soft plates for the case where the density of fixed charges within the polyelectrolyte layer is low. The interaction between two parallel cylinders and that between two crossed cylinders are considered. The obtained expression covers various limiting cases that include hard cylinder/hard cylinder interaction, cylindrical polyelectrolyte/cylindrical polyelectrolyte interaction, soft cylinder/cylindrical polyelectrolyte interaction, soft cylinder/hard cylinder interaction, and cylindrical polyelectrolyte/hard cylinder interaction. (c) 2008 Elsevier Inc. All rights reserved.