After chloroform extraction in an alkaline solution, diethylcarbamazine (DEC) is measured in the presence of dipropylacetamid (internal standard), treated in the same manner, by a gas chromatographic procedure using a nitrogen detector in a 10% BDS column. Results can be easily reproduced for analysis of DEC in sera up to levels of 10 mg/1 and sensibility allows determination of approximately 0.5 mg/l levels on 50-microliter samples of serum. This method is suitable for pharmacokinetic studies.