The aim of this study was to compare the performance of the automatic TEST 1 ESR system, SIRE Analytical Systems (TEST 1), with that of the the Sedisystem 15, Becton Dickinson (SEDI), and the International Council for Standardization in Haematology reference method (Westergren) for measuring the length of sedimentation reaction in blood (LSRB). This reaction was measured in 418 paired blood samples drawn in K2-EDTA vacuum tubes and specific tubes from patients scheduled for routine LSRB measurement. The TEST 1 system uses micro-sedimentation and quantitative capillary photometry technology, whereas the SEDI uses a CCD camera. For Westergren, a 200 mm column with 3.0 mm internal diameter was used. Compared to Westergren, TEST 1 gives accurate values of LSRB in most of the samples (mean of differences: 0.99 +/- 10.4 mm; 95% CI, -0.807 to 2.78 mm; n =131). Similar results were obtained in the comparison with SEDI (mean of differences: -0.626 +/- 8 mm; 95% CI, -1.756 to 0.5 mm; n = 195). Compared to those of fresh blood samples, LSRB values were significantly lower in 24 h stored samples, either at 4 degrees C (21.5 +/- 2.3 vs. 19.4 +/- 2.2 mm; p (Spearman's coefficient of correlation): 0.981; n = 44) or at room temperature (19.1 +/- 2.5 vs. 16.2 +/- 2.1 mm; p: 0.903; n = 46). In conclusion, TEST 1 is a rapid, reliable system for automatic measurement of LSRB in standard K2-EDTA blood samples. It has a very low imprecision and maintains a good performance in 24 h stored samples. In addition, due to its operational characteristics (60 samples/20 min) it is a suitable tool for clinical laboratories with a high work load as well as for emergency laboratories.