Recent studies in man and animal models have demonstrated that TCR-gamma delta-bearing T cells (gamma delta T cells) are activated by mycobacteria and accumulate in the sites of mycobacterial infection. Although the function of gamma delta T cells remains unclear, some data suggest a potential role for these cells in the granulomatous immune response. To address the presence of gamma delta T cells within the BCG granulomas, we have characterized the TCR phenotype of T-lymphocytes present in the BCG granulomatous lesion immunohistochemically using a monoclonal antibody to TCR delta 1 and others. Fairly large numbers of gamma delta T cells were located at the periphery of the BCG granulomas without necrosis and most of them also expressed CD8. However, gamma delta T cells were rarely present in the granulomas with central caseous necrosis, calcification and fibrotic changes. With these results, it might be speculated that the CD8+ gamma delta T lymphocytes participate in the BCG granuloma formation mainly in the early stage.