A semi-automated new methylene blue method for reticulocyte counting was compared to the manual method and fluorescence flow cytometry. Over a wide range of reticulocyte counts (0.3-12.7%) the new methylene blue method was found to be comparable to that of fluorescence flow cytometry, with high precision. Between-run precision studies showed coefficients of variation (CVs) of 4.8, 6.9 and 14.5% for reticulocyte counts of 9.5, 2.4 and 0.7%, respectively. Within-run precision studies showed CVs of 8.6, 8.1 and 6.1% for reticulocyte counts of 0.9, 5.3, and 18.4%, respectively. The correlation coefficient between the Coulter method and the manual method was 0.83, and 0.85 between the Coulter method and flow cytometry. The possibility of extending the incubation time to at least 4 h and the insignificant changes observed with samples stored for up to at least 72 h at 4-8 degrees C make this new method most convenient and allow any laboratory having Coulter STKS or MAXM cell counters to perform reticulocyte counts in an efficient, reliable manner.