This study will provide individuals who meet criteria for panic disorder with five weekly sessions of cognitive-behavioral therapy lasting one to one-and-a-half hours each. During these sessions, patients will receive information on the nature of panic disorder and a model of treatment and will receive weekly training in how to become more comfortable with sensations of anxiety, with the goal of preventing sensations of anxiety from escalating into panic. As part of this training, patients will practice ways of creating and then becoming comfortable with symptoms in and out of the therapist's office.

For the third, fourth, and fifth sessions of the five-session program of cognitive-behavioral therapy, the patient will be asked to arrive one hour early to take one of the study pill, a 50mg pill of either d-cycloserine or placebo, which participants will be randomly assigned to. A physician will be available in the unlikely event that a patient begins to experience side effects. Before the treatment starts, before the fourth session, and one week after the final session patients will have their levels of symptoms assessed with measures of mood, anxiety, and avoidance.

Upon completion of the study, participants will be asked to return for a one-month, two-month, three-month, and six-month follow-up.