Despite so much research on high performance concrete, the properties of this concrete are not known as well as those of ordinary concrete. There have been a lot of equations, rules and suggestions in the codes which are used in the design of reinforced concrete and prestressed concrete structures. They are obtained from experimental studies made on concrete that have compressive strength of less than about 40 MPa. It is not exactly known whether they could be used in the design of structures constructed by using high performance concrete. Therefore in this study, stress-strain and equivalent block parameters were obtained from experimental stress-strain diagrams for calculation of high performance reinforced concrete beams in flexure. The conclusions obtained from this study showed that determined rectangular stress block parameters can be used in the design of high performance reinforced concrete members in flexure. (C) 2002 Elsevier Science Ltd. All rights reserved.