In this study the hematological and biochemical parameters in the blood of indigenous Croatian working horse breeds were investigated. The Posavina and Croatian Coldblood horses are adapted to harsh environmental conditions and their blood parameters might differ from other horse breeds. The study was carried out on 100 mares and 12 stallions of ages from 2 to 19 years. Fifteen hematological and 19 biochemical parameters were analysed. Values of 22 parameters showed considerable overlapping with values obtained for other horse breeds, and substantial resemblance is evident with values reported for Pakistani working horses. Several reference values showed statistically significant effect of sex (Hb, ALB, CREA, TBIL and Ca where significantly higher in stallions; EOS, CK, ALP, UREA and Mg were significantly higher in mares). None of the parameters studied showed any differences associated with age. The adaptation of Posavina and Croatian Coldblood horses to the harsh environment of flooded pastures and the way of breeding might be reflected in their specific reference values. The obtained results enabled the establishment of hematological and biochemical reference values in the blood of Posavina and Croatian Coldblood horses that will in turn support clinical diagnosis and further research into horse physiology.