Antibiotic bioavailability is unpredictable in burnt patients due to altered distribution and clearance, with a high risk of either suboptimal or toxic levels. This study was aimed at assessing plasma levels of antibiotics administered to children with critical burn injuries, and at analyzing their relationship with a series of relevant variables. Over a two-month period, all children sustaining burns of over 20% body surface area, admitted to the Burn Unit at the Hospital de Pediatria “Juan P. Garrahan” and treated with Vancomycin and /or Amikacin were studied. 25 serial samples for drug peak and trough plasmatic levels, albumin, urea and creatinine were obtained. Antibiotic plasma levels showed great variability. Given an average dose of 41.25mg/kg/day Vancomycin, 66% of cases did not reach therapeutic levels(X=15.30mcg/ml), while the remaining 33% showed potentially toxic levels(X=67.36mcg/ml). Trough levels fell within the expected range in only 2 cases, 75% of samples falling below 8mcg/ml. All Amikacin levels obtained following an average dose of 16.15mg/kg/day were below the therapeutic range(X=7.89mcg/ml for peaks and X=0.65mcg/ml for trroughs). Using multiple regression, Vancomycin levels showed correlation with serum albumin (R=0.84 for peaks and R=0.69 for troughs; p<0.05). As for Amikacin, peaks correlated with the given dose (R=0.83; p<0.001) and troughs with serum creatinine (R=0.73; p<0.01). Taking into account that sepsis and multiple organ system failure are main causes of death in burn victims, antibiotic dosage must be serially monitored and readjusted in these patients.