To determine the rate and factors that affect carbamazepine absorption, six patients being treated in the pediatric intensive care unit for frequent seizures received loading doses (7.4 to 10.4 mg/kg) of carbamazepine suspension by either nasogastric or nasoduodenal tube. Carbamazepine serum concentrations were determined 15, 30, 60, 120, and 480 minutes after administration by fluorescence polarization immunoassay. One patient who had an ileus did not attain therapeutic concentrations (greater than 4.0 mg/L). The other five patients with normal gastrointestinal function achieved mean serum concentrations at 1 hour and 2 hours of 4.3 mg/L and 7.3 mg/L, respectively. Delayed gastric emptying and concurrent enteral feedings appear to slow the absorption of carbamazepine. No adverse effects were observed. Rapid loading with carbamazepine suspension appears to be a useful alternative for the management of critically ill pediatric patients who are experienced frequent seizures.