The subacute ruminal acidosis (SARA) is believed to play an important role in highproducing dairy farming. It is linked to low milk fat, low BCS, moreover laminitis and other kinds of pathology leading to high-culling rate on herd-level. Prevalence up to 40% in single herds has been reported from the US. In order to evaluate the prevalence of SARA in dairy herds under northwest European circumstances, 18 dairy herds in the Dutch province of Friesland had been selected in cooperation with a private veterinary practice for the study. In total, samples of ruminal fluid, milk, blood and urine were drawn from 197 individuals. Ruminal fluid was collected by means of ruminocentesis (rumen puncture). Ruminal fluid pH was determined immediately with a portable pH-meter and ruminal fluid quality was scored in different parameters. All fluids underwent laboratory analysis. All animals were scored for body condition, faeces quality, and rumen motility, filling and stratification. Additionally, 139 cows had been scored for body condition about six weeks prior to examination. The overall prevalence of SARA was found to be 13.7%. In cows up to 25 days post partum, 11% experienced SARA; the prevalence was 18% in cows longer in lactation. The difference, however, proved not to be significant. On 10 farms cows experiencing SARA were found, the prevalence per farm was between 8% and 38%. Correlations of ruminal pH were found with BCS and change of BCS, GLDH-plasma values, urine pH, net acid-base secretion and SCFA in ruminal fluid. The correlation of milk fat percentage with ruminal pH proved not to be significant statistically. On farm level, high milk production did not put cows at higher risk for SARA. SARA is present in dairy herds as found in the province of Friesland and the prevalence on certain farms is considerable. SARA has to be expected in situations of severe negative energy balance and might be traced in herds with low body condition scores and heavy condition loss after calving. Milk fat depression was only ...