In this paper, we first clarify some issues inherent in requirements analysis for safety-critical systems and indicate the importance of such notions as environment model, traceability, and well-grounded decisions. Secondly, we discuss the use of requirements engineering techniques in design processes of safety-critical systems. Finally, we give an account of an experiment in which requirement engineering processes are applied to the specification of a level-crossing control system, a typical safety-critical system in railways.