The aim of this paper is to propose a new way to calculate the chemical potential for dense systems containing flexible chain molecules by a Widomtype insertion technique. The method makes use of the self-avoiding randomwalk algorithm of Rosenbluth and Rosenbluth. We report some results for the calculation of the chemical potential for a simple monolayer system, originally simulated by Whittington and Chapman. To our knowledge, the chemical potential of a chain system has never been calculated before using a direct approach.