The objective was first to evaluate the performance (intra- and inter-assay imprecision, inaccuracy, detection limit and overlap performance) of two different commercially available human C-reactive protein (CRP) immunoturbidimetric assays (TIA) applied to porcine serum CRP; and secondly to investigate inter-laboratory discrepancies and the influence of calibration materials when comparing results. The intra-laboratory performance seemed acceptable for clinical purposes for both assays with excellent overlap performance, acceptable detection limits, no significant inaccuracies and low imprecision. Although a significant discrepancy in the measured CRP levels was observed when comparing results, the methods agreed significantly on diagnostic classification, suggesting a low clinical significance. Both assays performed reliably for the heterologous determination of porcine serum CRP for clinical purposes. The results emphasise the need to establish species-specific standards to decrease inter-laboratory discrepancies.