The goal of the study was to describe with prospective methodology the therapeutic response to nortriptyline in the respiratory panic disorder (PD) subtype versus the non-respiratory subtype. A total of 118 PD outpatients (DSM-IV) were previously divided into respiratory (n=77) and non-respiratory (n=41) subtypes and then treated with nortriptyline for 1 year. Demographic and clinical features were compared in the two groups. Anxiety scales were administered before and during the treatment by raters who were blind to the subtype diagnosis. The principal instruments used to evaluate response were the Clinical Global Impression, the Sheehan Panic and Anticipatory Anxiety Scale, and the Panic Disorder Severity Scale. In the first 8 weeks of treatment (acute phase), the respiratory subtype had a significantly faster response on all the major scales. At the end of the study (week 52), there was no difference in the scale scores, and the reduction in panic attacks from baseline to end-point did not differ significantly between the two groups. In the respiratory subtype, the disorder had a later onset, was associated with a high familial history of mental disorder, and significantly more often required treatment with more than an occasional benzodiazepine. The non-respiratory subtype had significantly more previous depressive episodes. In conclusion, the respiratory PD subtype had a faster response to treatment with nortriptyline at 8 weeks than did the non-respiratory subtype, and an equivalent response after 1 year of treatment.