Investigations have been conducted to the factors which have influence on the red blood count in postparturient sows. 147 blood samples of sows have been collected for the analysis of the influence of the number of lactations and puerperal diseases and 87 samples out of the collected blood samples were of healthy sows used to the analysis for the influence of the week of lactation. With rising number of lactations decrease the number of erythrocytes, packed cell volume and haemoglobin concentration, whereas mean corpuscular volume and mean corpuscular haemoglobin concentration rise. No significant changes of red blood count occur in the course of lactation. The number of erythrocytes and the packed cell volume decrease due to puerperal diseases. Hematological values of healthy postparturient sows are: erythrocytes: 5.8 +/- 0.6 T/l; packed cell volume: 0.41 +/- 0.03 l/l; hemoglobin concentration: 7.64 +/- 0.67 mmol/l; mean corpuscular volume: 71.4 +/- 5.8 fl; mean corpuscular hemoglobin: 1.30 +/- 0.9 fmol; mean corpuscular hemoglobin concentration: 18.3 +/- 0.8 mmol/l.