The Spacelab Life Sciences 2 mission (SLS-2) is the second in a planned series of dedicated Life Sciences missions utilizing the European Space Agency-provided Spacelab module. The mission, tentatively scheduled for a mid-1992 launch, will comprise a total of eighteen experiments encompassing both human and animal research. Eight of the eighteen experiments will involve animal life sciences research and will be managed by the Space Life Sciences Payloads Office (SLSPO) at NASA's Ames Research Center (ARC). The ARC payload complement of eight experiments will include six which use rodents and two which use primates (squirrel monkeys).SLS-2 provides an opportunity for even more extensive investigations into the effects of weightlessness upon the anatomy and physiology of rodent and primate systems. The SLS-2 ARC payload will build upon the previous success of the SL-3 mission, on which 24 rodents and 2 squirrel monkeys were flown, and the expected flight of SLS-1 in 1990, which will include 29 rodents and a number of jellyfish specimens. Experiments will be conducted to assess rodent cardiovascular and vestibular system responses to weightlessness, rodent and primate metabolic responses, and primate thermoregulation.Major hardware elements which will support the SLS-2 ARC Payload are two rodent Research Animal Holding Facilities (RAHFs) housing 24 animals each, one primate RAHF housing 4 squirrel monkeys, the General Purpose Work Station (GPWS), and the Small Mass Measuring Instrument (SMMI). The GPWS provides an enclosed, laminar-flow workbench for conducting some of the more complex rodent experiments featured on SLS-2. The primate RAHF will allow researchers an opportunity to obtain blood and urine samples, an opportunity not available on previous Spacelab missions.