Reproduction of the fruit fly, Drosophila melanogaster was examined in various combinations of oxygen concentration and total atmospheric pressure in an effort to establish extremes within which continued reproduction can take place. The effects of temperature were also examined. At 760 torr total pressure, it was found that reproduction could take place between 10% oxygen, PO2 = 76 torr, and 38% oxygen, PO2 = 288 torr, at a temperature of 26 degrees C. At 18 degrees C, the lower limit remained the same but the upper limit rose to 60% oxygen, PO2 = 456 torr. In hypobaric atmospheres totalling 250 torr, the low extreme was 30% oxygen, PO2 = 75 torr, and the upper level was 80% oxygen, PO2 = 200 torr. Because closed ecology life support systems proposed for future space programs will include similar small organisms with short life cycles, the author encourages similar reproductive studies with species most likely to accompany humans into space.