Five experiments that examined Wegner's theory of ironic processes of mental control in reactive motor performance under pressure are presented for the first time. In Experiments 1, 2, and 4, the authors conducted specific examinations of the incidence of an ironic error using a reactive motor task. In Experiments 3 and 5, they provided the first tests of whether task instruction moderates the incidence of ironic errors. The task required participants to react to a series of three primary-colored balls as they rolled down a chute under low-and high-anxiety conditions. Measures of anxiety, heart rate, heart-rate variability, and muscle activity confirmed the effectiveness of the anxiety manipulation. Experiments 1, 2, and 4 revealed that anxiety increased the number of ironic errors. In Experiments 3 and 5, the authors provided the first evidence that instructional interventions can reduce the incidence of anxiety-induced ironic performance errors in reactive motor tasks.