BACKGROUND: The serum K level is normal or high in the majority of patients with diabetic ketoacidosis (DKA) despite significant total body K+ deficits. This might be due to the combined effects of severe acidosis, insulin deficiency, volume contraction, hyperglycemia and hypertonicity that usually accompany DKA. The aim of this study was to investigate the most likely determinants of the serum K+ levels among metabolic derangements observed in DKA patients. METHODS: The subjects were 88 DKA patients who had normal or high initial serum K+ levels. We anaylzed the correlation between initial serum K' levels and metabolic parameters (arterial pH, arterial HCO(3-) level, anion gap, serum glucose level, osmolality, BUN and fasting C-peptide levels), by simple linear regression analysis and stepwise multiple regression analysis. RESULT: Serum K+ levels correlated significantly with initial arterial pH(r=-0.38, p<0.001), HCO(3-) (r=-0.35, p<0.001), anion gap(r=0.21, p<0.05), serum glucose (r=0.22, p<0.05) and fasting C-peptide (r=-0.33, p<0.05) levels. Among these, arterial HCO(3-), serum glueose and fasting C-peptide levels had significant and independent effects on serum K+ levels. These levels could account for about 33% of the observed variance in serum K+ levels. CONCLUSION: These results suggest that metabolic acidosis and hyperglycemia in DKA, which result primarily from insulin deficit, are the main determinants of increased serum K+ levels.