The observation was carried out in a group of 70 female cattle in the course of two years. The animals were kept in suckler herds. They were provided with pasture grass and maize silage indoors during the grazing season and with forage ration (silage and hay) in winter. The aim of the study was to assess the effect of year (2001 and 2002), season (spring and autumn), breed (Aberdeen Angus AA, Beef Simmental BS, Blonde d'Aquitaine BA, Charolais CH, Hereford HE and Limousin LI) and reproduction cycle (pregnant heifers PH, non-pregnant heifers NPH, pregnant cows PC, non-pregnant cows NC and lactating cows with calves LCC) on some blood plasma parameters. Mean values of these parameters were following: Total protein 72.37 gl⁻¹ , glucose (Glu) 3.23 mmol∙l⁻¹, urea (Urea) 4.39 mmol∙l⁻¹, bilirubin (Bilir) 4.63 mmol∙l⁻¹, alkaline phosphatase (ALP) 1.02 µkat∙l⁻¹, asparate aminotransferase (AST) 1.29 µkat∙l⁻¹, gamma glutamyltransferase (GMT) 0.30 µkat∙l⁻¹, sodium (Na) 114.33 mmol∙l⁻¹, calcium (Ca) 2.30 mmol∙l⁻¹ and phosphorus (P) 1.99 mmolT1. Year affected TP, Glu, Bilir, ALP, AST (all p<0.01) and urea (p<0.05). Season affected TP, Glu, urea, Bilir, Ca, P (all p<0.01) . There were significant differences in urea, GMT, Ca and P between breeds. Reproduction cycle affected TP and Glu (p<0.05). It can be concluded that year and season affected the observed blood plasma parameters considerably more than breed or reproduction cycle.