The major goal of medical investigations in the USSR longterm (up to 6 months) manned space flights was to accumulate information on human responses to prolonged weightlessness. Before, during and after these flights, detailed clinical, physiological, immunological and anthropometric examinations were conducted. The examinations demonstrated that man may well adapt to long-term space flight, retaining good health and a high work capacity. The changes seen postflight were reversible and disappeared completely after a relatively short readaptation period. Postflight changes did not correlate with the flight duration. A reasonable work-rest cycle and various physiological countermeasures were used, the efficiency of which were substantiated by means of regular medical examinations. These methods helped the cosmonauts to maintain good health status and adequate performance inflight and facilitated their readaptation postflight. Medical investigations performed during the Salyut-6 flights indicate that the duration of manned space flight can be increased.