The performance characteristics of an analytical method based on high-performance liquid chromatography (HPLC) for the detection of the banned growth promoters, carbadox and olaquindox, in feedstuff were determined via a collaborative study. The relative standard deviation of repeatability (RSDr) ranged 1.1-5.5% for carbadox and 2.5-6.2% for olaquindox. The relative standard deviation of reproducibility (RSDR) ranged 6.4-10.7% for carbadox and 12.8-20.0% for olaquindox. In all cases, the HORRAT values were equal or below the critical value of 1.5. Moreover, trueness in all cases was between the acceptance limits of 80 and 110%. Consequently, it was concluded that the method is suitable for quantitative evaluation. The method was also qualitatively assessed in terms of correct identification of the target analytes by examination of the UV spectrum when the more specific diode array detector was coupled to HPLC. In all cases, the percentage of correct identifications was >or=94% for olaquindox and carbadox, while the percentage of false negatives was <or=6%, suggesting the extended utilization of the HPLC method from quantitative to confirmatory status with a diode array detector.