Ketosis is still an important problem which must be solved in dairy herds. Early precise diagnosis and proper evaluation of the cause of the disease is essential for good management of ketosis on dairy farms. The aim of our work was to analyse the occurrence of rumen dysfunction in connection with subclinical ketosis in dairy herds and to evaluate the relationships between beta-hydroxybutyrate (BHB) concentration in blood and metabolic parameters in blood, urine and rumen fluid. We analysed the results of metabolic profile tests performed in dairy cattle herds from 1,338 cows. The concentration of BHB significantly correlated with glucose, NEFA (nonesterified fatty acids), bilirubin, AST (aspartate aminotransferase), GGT (γ-glutamyl transferase), urea, magnesium and calcium in blood serum and with following parameters of rumen fluid – acetate, propionate, butyrate, acetate/propionate and infusoria. Significant but weak correlations were found between BHB and urine parameters (pH, specific gravity, potassium, magnesium, chloride). Subclinical ruminal acidosis was found in 23.1% and 16.7% of dairy cows with light (BHB 1.2–2 mmol/L) and more severe subclinical ketosis (BHB >2 mmol/L) and simple ruminal indigestion in 16.7% and 30%, respectively. On the basis of performed analysis we can conclude that rumen dysfunction is an important factor for the development of ketosis. Veterinary practitioners should suggest checking the feeding management in their diagnostic work with the aim to distinguish primary and secondary ketosis. Only complex and precise diagnostic work allows applying correct and successful therapy not only for individual animals but also for herd health management.