Background Over one million soldiers were treated for battle- or training-fatigue during World War II.Of all groundcombat troops,37％ were discharged for psychiatric reasons due to fatigue.The neuroendocrinological and immunological systems played important roles in the work-related fatigue of military personnel.The aim of this study was to investigate the characteristics of fatigue associated with military operations,and we observed changes in the regulatory functions of the neuroendocrinological and immunological systems that may provide theoretical support for improving the combat effectiveness of armies.@@Methods A total of 240 soldiers from the Field Artillery regiment were selected as subjects.Researchers and subjects received training before participating in the study.Data of the subjects' medical histories,physical examinations,scores on a fatigue assessment scale,and assessments of pituitary-adrenal hormones (adrenal cortical hormone (ACTH),cortical hormone (F),and 24-hour urine-free cortisol (UFC)),pituitary-gonadal hormones (luteinizing hormone (LH),follicle-stimulating hormone (FSH),testosterone,estradiol (E2),and prolactin (PRL)),pituitary-thyroid hormones (thyroid-stimulating hormone (TSH),thyroxine (-I-r4),triiodothyronine (I-T3),free thyroxine (FT4),and free triiodothyronine (FT3)),and cellular immune parameters (CD3+,CD4+,CD8+,CD4+/CD8+,B,and NK cells) were investigated before and after large-scale and high-intensity field exercises.Data were statistically analyzed with Student's ttest using SPSS software (version 13.0),and Pvalues