Orthostatic tolerance of the Salyut-4 crewmembers was measured by means of LBNP tests (--25 mm Hg for 2 min and --35 mm Hg for subsequent 3 min). Orthostatic tolerance decreased, remaining, however, satisfactory throughout the 2-month flight. During LBNP tests the pattern of most cardiovascular changes inflight and on the earth was similar. In weightlessness heart rate increased reaching maximum preflight values; cardiac output and stroke volume decreased noticeably; the systolic time interval changed significantly. The recommended regimen of LBNP did not deteriorate the health state of the crewmembers and was adequate to predict their orthostatic tolerance. Criteria for the evaluation of the health condition of space crewmembers were developed.