The present study was undertaken to examine the role of the exercise-induced stress hormone response on the regulation of type 1 and type 2 T lymphocyte intracellular cytokine production. Subjects performed 2.5 hr of cycling exercise at 65% maximal O₂ uptake while ingesting a 6.4% carbohydrate (CHO) solution, 12.8% CHO solution or a placebo. Peripheral whole blood samples were stimulated and stained for T lymphocyte surface antigens (CD4 and CD8). Cells were then permeabilised, stained for intracellular cytokines and analysed using flow cytometry. Exercise resulted in a decrease (P<0.05) in the number and percentage of IFN- positive CD4⁺ and CD8⁺ T lymphocytes. These stimulated cells produced less IFN- immediately post-exercise (P<0.05) and 2-hr post-exercise (P<0.05) compared with pre-exercise. However, CHO ingestion, which attenuated the exercise-induced stress hormone response compared with placebo (P<0.05), prevented both the decrease in the number and percentage of IFN- positive CD4⁺ and CD8⁺ T lymphocytes, and the suppression of IFN- production from stimulated CD4⁺ and CD8⁺ T lymphocytes. There was no effect of exercise on the number of, or cytokine production from, IL-4 positive CD4⁺ or CD8⁺ T lymphocytes. These data provide support for the role of exercise-induced elevations in stress hormones in the regulation of type 1 T lymphocyte cytokine production and distribution.