After reviewing more than 6000 clinical charts of patients who received vancomycin therapy and whose serum vancomycin level was monitored between January 2010 and December 2013, we identified 212 patients who also had diagnosed as severe acute pancreatitis (SAP group), and 98 patients who also had diagnosed as pneumonia (pneumonia group) at that time. The fluorescence polarization immunoassay method was used to measure vancomycin serum trough concentrations in these patients 30 min before the next administration. Using these measurements, we calculated the pharmacokinetic parameters using the Bayesian estimator.