During 18 years (since January 1955) short and long term fluctuations in the physico‐chemical state of the blood of healthy male blood donors have been studied by the Biometeorological Research Centre in Leiden, since 1966 also in Oslo and since 1968 in 16 other bloodbanks in the N. and S. hemisphere. The total number of data received per year varies between 100,000 and 150,000. Of the 18 different blood parameters studied, particularly blood sedimentation rate (BSR), haemoglobin (Hb), serum albumin and γ‐globulin and diastolic blood pressure (DBP) showed interesting fluctuations. The most interesting fluctuations are observed in the BSR patterns. They show short (daily or weekly) and long term changes, either monthly (seasonal or pseudo‐seasonal) or very long term yearly changes with periods of probably 3, 6 and 11 years. Short term changes correlate significantly with the degree of atmospheric cooling. The BSR patterns show also geographical differences. From South to North (in the N. hemisphere) the BSR values seem to become smaller. The same occurs with increasing altitude. This lowering of BSR values is due to the reduced fibrinogen content of the blood and may be caused by reduced infrared radiation, changes in UV radiation and decreasing average temperature from the equator to the poles.