Abstract: A previously suggested simple relationship in a diagram of(Al₂O₃ vs. MgO + FeO + Fe₂O₃)_opx for the distinction between igneous and metamorphic orthopyroxenes is shown to be inadequate. A revised diagram is presented and its limitations are discussed. A diagram showing Fe²⁺/(Fe²⁺ + Mg) vs. 100Ca/(Fe²⁺ + Mg + Ca) for orthopyroxenes coexisting with Ca-rich clinopyroxenes proves to be useful for the discrimination of igneous and metamorphic orthopyroxenes and for evaluation of the extent and physical conditions of regional orthopyroxene re-equilibration.