We undertook the present study to examine the acid-base and electrolyte disturbances in relation to hydration status in patients with diabetic ketoacidosis (DKA). A total of 40 insulin-dependent diabetes mellitus patients (22 male, 18 female), aged 18-61 years with DKA admitted to our hospital during the last 2 years, were studied. The duration of diabetes averaged 9 +/- 2 years. In all cases a detailed investigation of the acid-base status and electrolyte parameters was performed. Twenty-one patients had a pure metabolic acidosis with an increased serum anion gap, seven had DKA combined with hyperchloremic metabolic acidosis, nine had DKA coexisting with metabolic alkalosis, while three had DKA with a concurrent respiratory alkalosis. Hydration status as evidenced by the ratio of urea/creatinine seems to play an important role in the development of mixed acid-base disorders (detected by changes in the ratios delta anion gap/delta bicarbonate (delta AG/delta HCO3) and sodium/chloride (Na/Cl)). In fact, hyperchloremic acidosis developed in the patients with the better hydration status. However, contradictorily, the severely dehydrated patients who experienced recurrent episodes of vomiting developed DKA with a concurrent metabolic alkalosis. Finally, patients with pneumonia or gram-negative septicemia exhibited DKA combined with a primary respiratory alkalosis. We conclude that patients with DKA commonly develop mixed acid-base disorders, which are partly dependent on patients' hydration status.