The objective of this study was to ascertain the relationship of alprazolam plasma levels and an anxiety-prone cognitive style to the characteristics and severity of early withdrawal after abrupt discontinuation of alprazolam in 26 patients with panic disorder. After 8 and 9 weeks of fixed-dose treatment, patients were hospitalized for 24 hours. On 1 admission, ordered at random, treatment was maintained; on the other, placebo was substituted double blind. The Anxious Thoughts and Tendencies questionnaire was administered before treatment. Alprazolam plasma levels were measured 7 times on the day after each admission. Before each blood sampling, the Profile of Mood States and performance tasks were administered, and vital signs were recorded. On the day after abrupt discontinuation of alprazolam, Profile of Mood States anxiety, depression, fatigue, and confusion increased; vigor and elation decreased; speed on the digit symbol substitution task improved; and systolic blood pressure increased substantially over time. High Anxious Thoughts and Tendencies scores were related specifically to more anxiety. Our findings (1) confirm that dysphoric mood, fatigue, low energy, confusion, and elevated systolic blood pressure are part of the early syndrome of withdrawal from alprazolam in patients with panic disorder, notably as the drop in plasma levels approaches 50%; (2) indicate a psychomotor deficit persisting beyond dose stabilization; (3) suggest that an anxiety-prone cognitive style measurable before undertaking treatment may be a risk factor for more severe anxiety upon discontinuation; and (4) provide a rationale for applying cognitive behavior therapy during benzodiazepine taper.