The results on boiling of liquids and gas bubbling under simulated long-term reduced gravity are reported. The possibility of extrapolating these results to the real spacecraft conditions is considered and the program of on-board space experiments is proposed to test the current theory at the relative accelerations10−4–10−6which are unattainable in a laboratory. Tests in free-fall towers, in aircraft, or in ballistic rockets are inadequate since only prolonged (over one hour) experiments in the Earth’s orbit can provide reliable data. The advantage of cryogenic liquids, helium, in particular, in space experiments is discussed. ©1998 American Institute of Physics.