SEXUAL DESIRE is one of the most important and the same time most potent motives in human beings. According to Islamic teachings fasting can reduce its potency If this is true, is it accomplished by a reduction in plasma testosterone level? These questions are addressed by the present study. Thirty-two healthy and single male subjects (age range 24-28 yrs) went under the study During the holy month of Ramadan, they avoided foods and drinks for about 12 hrs, according the Islamic fasting program. Three blood samples were taken from each subject at 5 pm respectively in the day before Ramadan (baseline sample), 1st and last day of Ramadan. Plasma testosterone, FSH and LH levels were determined by radioimmunoassay. In addition, all subjects, filled out a question er: which searched for changes in SEXUAL DESIRE. Testosterone levels in 2nd and 3rd test samples were signifier ntly greater than the baseline one (p<O.05). No traceable change occurred in LH levels, but FSH showed si6"nificant reduction in 2nd and 3rd samples (p<O.05). There was also a significant reduction in SEXUAL DESIRE during Ramadan (p<O.05). The reverse changes occurred between plasma testosterone levels and SEXUAL DESIRE during Ramadan deserves attention. This possibly suggests, dominant psychological influence acting inside the CNS, on SEXUAL DESIRE during Islamic fasting rather than effects elicited by testosterone peripherally.