Stress can produce immunosuppression leading to increased susceptibility to infection, tumor growth or autoimmune disease. It has been recently noted, however, that certain kinds of stress need not increase the risk of immune pathology. The present study looked for immune pathology in an anxiety-related disorder. Acute exacerbation of obsessive-compulsive disorder (OCD), an anxiety spectrum disorder, served as a model for stress. Seven OCD subjects in acute exacerbation, and 9 healthy age-matched control subjects participated in the study. T cell subsets were determined at baseline in both OCD and control groups, and after 6 weeks on clomipramine in the OCD group. No statistically significant changes in lymphocyte subsets were found between the control and the untreated patient groups. Likewise, no statistically significant changes were found in patients before and after treatment. The negative finding of the present study supports the view that stress need not compromise immunologic function. Various aspects of stress, which may turn the immune system vulnerable, are discussed as well.