Stress induces an imbalance of neuroimmunomodulation, a phenomenon involving the immune, central nervous and endocrine systems. Receptors to substances involved in stress reactions and anxiety, like adrenaline, acetylcholine, histamine, endomorphines, ACTH and several neuropeptides, are present on lymphocytes and lymphocytes can secrete various hormones and neuropeptides. Peripheral and central, cortical and subcortical nervous structures influence immune response. Steroids play a dose dependent inhibitory role perhaps via GIF (Glucocorticoid Increasing Factor) and cytokines (IL 1). In rats, stress induces an increase of corticosterone levels and a lymphopenia depending on the presence of adrenals and pituitary, whereas functional responses to mitogens appear decreased in animals even after surgical removal of adrenals and/or pituitary. Immune response vary according to the degree of control over stressors, to the type of stressor and the animal species. Chronic or repeated stress tends to stimulate immune reaction, contrary to acute stress. In man grief reactions, terminal illness of a spouse, divorce, examinations, caregiving to Alzheimer patients have been used as models of stress, with immune consequences. Pathological anxiety has been less studied, with only few anomalies reported in DSM III-R panic disorder. The immune system participation in the adaptive response to stress is reviewed.