This study evaluated the performance of the HCG STAT Elecsys assay in 8 European laboratories using the Elecsys 2010 system. Analytical sensitivity was < 0.5 mlU/mL. The analysis of concentration series prepared by mixing serum pools with high and low HCG concentrations proved linearity up to 10.000 mIU/mL. A high-dose hook effect was not seen up to HCG concentrations of 430.000 mIU/mL. The medians of the within-run CVs (n = 21, 3 series) were 3.0% (2.1-5.8% CV; 10.4-14.4 mIU/mL), 2.4% (1.7-6.1% CV; 35.6-88.6 mIU/mL) and 2.3% (1.7-6.1% CV; 282.3-643.8 mIU/mL). The medians of the between-day imprecisions (n = 10-21) were 7.0% CV (5.2-12.0% CV; 4.0-14.0 mIU/mL), 5.5% CV (3.1-7.2% CV; 35.4-92.7% mIU/mL) and 4.1% CV (2.8-5.1% CV; 270.8-658.0 mIU/mL). The median recovery of two external quality control samples with assigned values of 9.39 and 10.40 mIU/mL) were 101.2 and 104.3% (ranges: 94.8-116.1%, 98.6-117.8%, n = 10). The assay was compared with five non-isotopic automated routine immunoassay systems (x). Slopes ranged from 0.87 to 1.15 and intercepts from-0.53 to 12.50 mIU/mL. The coefficients of correlation were with one exception (0.898) > or = 0.960. The distribution of HCG in samples from non-pregnant women and healthy men was very similar to that observed with other automated routine methods. The HCG Elecsys assay is very specific for the intact holo-hormone. Nicked HCG dimer, nicked and non-nicked beta-subunits are weakly recognised or not detected. Hemoglobin, bilirubin and lipemia (tested up to: Hb, 3.7 g/L; bilirubin, 500 mumol/L; triglyceride, 37.6 mmol/L) did not interfere the assay. The HCG Elecsys assay is well suited for the early and fast diagnosis of normal pregnancy and the detection of tubal pregnancy.