The aim of this study was to investigate the variations of some physiological parameters in dairy cows during subacute ruminal acidosis (SARA), a common important disorder of dairy cows that occurs in early lactation. pH changes in ruminal fluid collected by rumenocentesis were measured at ten farms stationed in different zones in the north of Italy. Additionally, the following parameters were measured: blood pH, faecal pH, urine pH, partial pressure of carbon dioxide oxygen, partial pressure of oxygen, bicarbonate level, base excess of extracellular fluid and oxygen content. Herds were divided into two groups according to their average ruminal pH: group A included farms with average ruminal pH > 5.8 (normal) and group B farms with average ruminal pH < 5.8 (acidosis). Unpaired Student’s t test was used to reveal statistical significances between the two groups. Ruminal pH changes due to pathogenesis can be diagnostic for SARA.