AIMS--To assess the distribution of gamma delta T-cells in the human bronchial tree; and to compare quantitatively the differences between gamma delta T-cell numbers in different parts of the airway wall in smokers and non-smokers. METHODS--Full thickness bronchial wall sections were taken from 10 whole lung specimens from both smokers and non-smokers. Serial cryostat sections stained with the monoclonal antibodies CD3 and TCR delta-1 were examined with the aid of interactive image analysis to assess gamma delta T-cell numbers both in absolute terms and as a proportion of total T lymphocyte numbers. RESULTS--In all cases gamma delta T-cells were demonstrable throughout the airway wall. Although in absolute terms they tend to occur predominantly in the bronchial epithelium, this seems to reflect higher numbers of T lymphocytes in the epithelium in general compared with the submucosa. No genuine epitheliotropism is evident. Comparison by smoking status shows a significant increase in gamma delta T-cell numbers in the bronchial glands of smokers compared with non-smokers. CONCLUSIONS--gamma delta T-cells form an integral though variable component of the immunocompetent cell population of the human airway in both smokers and non-smokers. Although epitheliotropism does not exist in the bronchial tree, gamma delta T-cells seem to form a significant part of the bronchial gland inflammation associated with smoking.