Differences were observed in hormonal levels between in both sexes of people living in Irbid City (620 meters above sea level) and in the Jordan Valley (360 meters below sea level). In addition, exercise was shown to differentially affect hormonal levels of both sexes at the above and below sea level locations. Serum levels of leutinizing hormone (LH) and testosterone (T) in adult male and serum levels of follicle-stimulating hormone (FSH) and progesterone (P) in adult female people were investigated in Irbid City and in the Jordan Valley during the years 1997 and 1998. The levels of these hormones were followed each month during this period. In males living in Irbid City, LH and T peaked from March through June, and in females at the same site, FSH and P also peaked from March through June. These data confirm the seasonal variation in sex hormones reported elsewhere in (wo)man and in other species. In males and females of the Jordan Valley, serum levels of LH, FSH, T and P were all higher than those of Irbid City throughout the year. Additionally, peaks of LH and T in male and FSH and P in female subjects in the Jordan Valley were observed from March through September. The high levels of these hormones and the extension of their peaks are suggested to be due to effects of the environmental factors of the Jordan Valley (high temperature, high barometric pressure) compared to those in Irbid City and other areas located at above sea level altitude.