Gamma-delta T (gamma delta T) cells form a subgroup which has been reported to play a role in both natural and acquired immunity. Their levels have been found to increase in some tumour tissues. The aim of this study was to investigate the ratio of gamma delta T cells to all T cells in the peripheral blood of advanced-stage cancer patients; the level of gamma delta T cells expressing the V delta 2-T-cell receptor (TCR) chain; NKG2D receptor expression; and apoptotic (Annexin-V) gamma delta T-cell levels. Twenty patients with advanced-stage cancer and 13 healthy controls were included. No statistical differences were found between control and patient groups in terms of the gamma delta T/total T-cell ratio (P=0.53), the V delta 2-TCR expressing gamma delta T-cell ratio (P=0.19) or the Annexin-V ratio (P=0.48). However, NKG2D expression in gamma delta T cells was significantly different between the control and patient groups (P=0.014). In summary it was shown that the levels of NKG2D receptors, which are responsible for the cytolytic effect of gamma delta T cells, were lower in cancer patients than in healthy adults. However, no significant differences were observed in the other parameters studied between groups.