A method for the calculation of the limits of detection (LD) and quantification (LQ) for the analysis of organochlorine compounds in serum is described. The method is based on the analysis of proficiency testing materials, an external quality assessment for selected pollutants, and the study of the signal/noise ratio of chromatograms obtained from GC-ECD injection. This method provides representative results for matrix effects, instrumental variability and extraction recoveries in the analysis of serum samples.