1. Anthropometric variables, resting heart rate and respiratory gas exchange were measured in twelve male and nine female Asiatic adult Moslems during the month of Ramadan, the week before and the month after Ramadan. 2. Energy intakes were estimated from dietary recall during fasting and non-fasting conditions. 3. Both male and female subjects experienced a decrease in body mass with the reduction in energy intake during fasting. Males experienced a greater reduction than females in resting heart rate; females lost more body-weight and subcutaneous fat than males. 4. Urine output and fluid intake were measured in twelve male subjects for 1 d during each week of fasting and 1 d during the pre-fasting control period. Among the subjects examined, the Ramadan regimen did not result in changes in the pattern of fluid exchange.