Abstract Objectives: To investigate the relation between plasma adenosine deaminase (ADA) activity and cytokine-producing T cells in preeclampsia. Design and methods: Plasma ADA activity and the proportions of cytokine-producing T cells were measured in peripheral blood of 28 women with normal pregnancies and preeclampsia. The proportion of CD4-positive T cells producing interferon-γ and interleukin-4 were analyzed by flow cytometry. Results: Plasma ADA activity in preeclampsia was significantly higher than that in normal pregnancy ( p < 0.05). In preeclampsia, the proportion of interferon-γ producing cells significantly increased, and the proportion of interleukin-4 producing cells was significantly decreased compared with normal pregnancy. A significant correlation was found between ADA activity and the proportion of interferon-γ producing cells in preeclampsia (r = 0.58, p < 0.05). Conclusions: Increased plasma ADA activity in preeclampsia may be in part associated with changes in the proportion of interferon-γ secreting cells.