It is reported that in both elite and recreational athletes Growth Hormone (GH) is the most commonly used drug aimed at improving sport performance. Aim: The purpose of the present study was to evaluate the immunomodulatory effects of short-term administration of recombinant human GH (rhGH) in healthy young males. NK cell number, activity and phenotype, T cell number, cytokine production of IL-2, IL-4, IL-6, IL-10, TNF-α and IFN-γ and CD4 + /CD8 + ratio with particular attention to the possible correlation to IGF-I production were investigated. Methodology: 30 healthy young males (27 ± 9 yrs) were randomly assigned to either placebo (n = 15) or drug (rhGH) 1mg/day groups (n = 15) with daily injection for seven days. IGF-I serum concentration and flow cytometry data were generated at baseline (day 0) and days 8, 15, 22 and 29 post injection. Data was analysed using a General Linear Model with repeated measures with a Bonferroni correction factor and significance set at p≤0.05. Results: The T cell cytokine secretion profile indicated a Th1 -Th2 shift. Interestingly, a significant difference (p≤0.05) of IL-10 mean fluorescence is noted from day 15 (P= 35.14; ± 19.93, rhGH = 26.63; ± 16.39) to day 22 (P= 61.32; ± 20.41, rhGH= 74.99; ± 46.91) and to day 29 (P= 101.98; ± 67.25, rhGH= 107.74; ± 122.58). Serum IGF-I concentration (ng/mL) increased significantly (p≤0.01) on day 8 (0.48 ± 0.78) after injections compared to baseline (0.31 ± 0.07) as well at day 15 (0.33 ± 0.06), 22 (0.29 ± 0.05) and 29 (0.29 ± 0.06). In conclusion, the cytokine secretion spectrum is affected by short-term rhGH administration in healthy young males being suggested to have induced CD4 + T lymphocytes production of IL-10.