It is known that severe acute respiratory syndrome (SARS), a severe infectious illness, which caused an epidemic in Asia in 2003, has extensive and complex effects on human organ systems. It has been reported that the serum levels of prolactin (PRL), follicle stimulating hormone (FSH), and luteinizing hormone (LH) of SARS patients are significantly higher than those of control groups, while estradiol (E2), pregnancy hormone (P), and thyroid stimulating hormone (TSH) are considerably lower than those of normal controls. This phenomenon suggests that the adenohypophyseal endocrine cells in SARS patients may be damaged. However, up to now there has been no direct histological investigation on the endocrine cells of patients' pituitary. Here we investigated the endocrine cells in the adenohypophysis obtained from autopsies of 5 SARS patients. The immunohistochemistry and quantitative image results showed that compared with control cases, both the number of positive cells and the staining intensity of immunoreactivity for growth hormone, TSH, and adrenocorticotrophic hormone in these cells were remarkably decreased, while that of PRL, FSH, and LH were significantly increased in all SARS cases studied. These findings indicated that alterations occurred in the patients' adenohypophyseal endocrine cells, and these changes were consistent with the serum levels of relevant endocrine hormones reported previously. It appears that changes in these endocrine cells and their hormones are affected by the severity of this new infectious disease.