In this paper we will address the success of Human Resource Management (HRM) implementation, concentrating not on the HR function but on first-line managers. First-line managers find implementing HR practices at the operational level difficult and show reluctance with their HR responsibilities. However, they have become increasingly responsible for the implementation of HRM and thus, their performance is critical for HRM effectiveness. Previous research pointed to five factors that could lead to HRM implementation difficulties. Four case studies in four different multinational business units are presented here to investigate the salience of these factors. Results show that first-line managers perceive four of the five factors hindering, but that the challenges faced vary per business unit.