While being banned in the European Union, the herbicide atrazine (ATR) is still one of the most used herbicides in the world. ATR is classified as an endocrine disruptor, but the immunotoxic effects of ATR may also be due to its direct impact on immune cells. To study the effects of ATR on human T cells, we activated T cells present in PBMCs of 8 healthy donors in the presence of ATR (0.1-100 μM). After 4 days of culture, T cells were stained to evaluate cell growth and phenotype by flow cytometry. The results demonstrated that ATR treatment exerts an antiproliferative activity on CD4