Tritiated imipramine (3H-IMI) binding was investigated in platelets obtained from nine patients suffering from panic disorder (PD), and from nine healthy controls (HC). IMI binding was studied according to a protocol provided by the WHO. Binding parameters, the maximum binding capacity (Bmax) and the dissociation constant (Kd), were measured after construction of the Scatchard plot. When the samples of the two groups were compared, significant differences between the Bmax of HC and PD were found. No significant difference was observed for the Kd. The investigation shows that panic disorder may influence 3H-IMI binding in platelets, suggesting an involvement of the serotoninergic system in this disorder.