The new fully automated reticulocyte analyzer, Sysmex R-1000 (TOA Medical Electronics, Kobe, Japan), was evaluated for its routine use in the Hematological Laboratory at the University Hospital Basel, Switzerland. The operating characteristics, such as within-run precision, linearity, and carryover, fulfilled the manufacturer's specifications and are excellent. Correlation with the standard method, manual reticulocyte counting, is linear for normal and high values. For low reticulocyte counts the regression points show a deviation from their linearity. An absolute zero value is not obtained by the R-1000. The R-1000 measures total RNA content of each cell and expresses the value as low fluorescence ratio (LFR), medium fluorescence ratio (MFR), and high fluorescence ratio (HFR). The analysis of this ratio resolves the problem of zero reticulocytes: A fraction of less than 0.002 (0.2%) with an LFR of 100% represents aplasia; a shift of the intensity of fluorescence to HFR heralds regeneration. Results of samples stored at room temperature remain stable and within the range of the within-run precision for up to 12 hours, when stored at 5 degrees C for more than 48 hours. The authors conclude that the R-1000 is easy to operate, fulfills the criteria for accuracy and precision, and is highly suitable for daily routine use in a large central hematologic laboratory.