Steel trusses and other structures with angle section members are usually designed by elastic methods. This may lead to uneconomical designs when these sections are subjected - besides the axial force - to biaxial bending arising not only from eccentric connections, but also from direct transverse loading. This paper provides a simple inelastic interaction formula, Eq. (14), as well as an enhanced inelastic formula, Eq. (27), for the combination of axial force and bending moments about the principal axes which may be used for angle cross-sections of classes 1 or 2. The formulae do not always exhaust the full plastic cross-sectional resistance but do lead to a more economical design of the section, especially when bending is dominant. The formulae cover only the design of the cross-section and do not address stability considerations.