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An instron technique was peveloped for determining leaf toughness of maize (Zea mays L.) and its relation to maize resistance to the European corn borer, Ostrinia nubilalis (Hûbner). Leaf tissue of field-grown maize was mounted onto a stainless steel plate, and the force required to puncture the leaf was determined using an instron. A rounded cylindrical probe attached to the instron gave consistent leaf-toughness readings. Significant negative correlations were found between leaf toughness and leaf-damage ratings taken at midwhorl and plant tasseling for five different groups of maize germplasm that included multiple borer-resistant cultivars and inbreds, Mexican landraces, BS9 selection cycles, and North American inbreds. Leaf toughness appears to be an important defense mechanism in maize across diverse groups of germplasm. Instron measurements of leaf toughness can be used to monitor leaf …