The aim of the study was to investigate acid-base changes and to determine some serum biochemical parameters in dehydrated calves with diarrhoea according to the degree of dehydratation. Thirty diarrhoeic dehydrated calves submitted to treatment in the university clinic, were used in the study. The calves were accessed as suitable for this study, if they were moderately or severely dehydrated according to clinical symptoms. All sick calves had the usual yellow and watery diarrhoea. Calves with 4% to 8% dehydration (moderate) had a weak suckle reflex, dry mucous membranes, warm mouth and partly good muscular tone. Calves with 10% and above dehydration (severe) were unable to stand, and had no suckling reflex and cold mouth. The mean pH, base excess, chloride (only severely dehydrated group) and sodium were significantly decreased in both moderately and severely dehydrated groups. On the other hand, potassium, phosphorus, HCO3- and anion gap levels were increased, compared to that of the control group. Results of this study showed that there was a relationship between the base excess and anion gap, with a degree of clinical dehydration. However, there may not be an exact correlation between the degree of dehydration and the severity of acidosis. Based on the clinical symptoms, the results of this study could be a useful tool under field conditions, in estimating the base excess in diarrhoeic dehydrated calves, when acidosis therapy is needed.