A total of 120 (80 males and 39 females) newborn Holstein-Frisian calves suffering from acute diarrhoea were studied clinically and biochemically, including the following parameters: pH, pCO2, act. HCO3, BE, RBC, PCV, HV, glucose lactate, urea, creatinine, total bilirubin, total protein, AST, Na, K and Cl. The results were interpreted according to their healthy condition, their age as well as their sex. The study had revealed an extreme metabolic acidosis, haemoconcentration, hypoglycaemia and hypofunction in the kidney and liver. Furthermore, the calves with diarrhoea had showed hyponatraemia, hypochloraemia, and hyperkalaemia. Important correlations between clinical and some blood parameters were found. Metabolic acidosis was more severe in male calves than females. These pathophysiological changes should be put in consideration during the therapy of newborn calves suffering from diarrhoea.