This study was conducted to examine lymphocyte subset counts and mood states in panic disorder patients. Twenty patients with panic disorder and 20 age- and gender-matched normal healthy subjects were recruited for the study. We used the Spielberger State (STAIS) & Trait (STAIT) Anxiety Inventory, Hamilton Depression Rating scale (HAMD) and Hamilton Anxiety Rating scale (HAMA) to measure mood states in all subjects. Lymphocyte subsets counts were made by flow cytometry. Panic patients showed significantly higher scores for anxiety and depression than normal subjects. Panic patients showed no differences in terms of the numbers of immune cells, as compared with normal healthy subjects, other than a lower proportion of T suppressor cells and a higher T helper cell/T suppressor cell ratio. HAMA and STAIS scores were common factors that could predict T cell numbers and proportions, T helper cell numbers, and natural killer cell proportions in panic disorder patients. We suggest that anxiety levels are related to the T-cell population in panic disorder patients and that quantitative immune differences may reflect altered immunity in this disorder.