Leukocyte subsets, serum cortisol and immunoglobulin production were investigated in a group of 12 migraine without aura patients, 12 chronic tension-type headache patients and compared with findings in 12 healthy controls. Chronic tension-type headache patients had statistically significant increased levels of B-lymphocytes (CD19+ cells) (p < 0.05), while migraine sufferers had a similarly significant decrease in CD8+ T-lymphocytes (p < 0.05). Migraine patients also had an increased percentage of B-lymphocytes although this failed to reach statistical significance. Immunoglobulin production and cortisol serum levels did not differ in the two headache groups. We conclude that the observed abnormalities in tension-type headache and migraine are unlikely to be a consequence of pain or of hypothalamic-pituitary-adrenal axis dysfunction.