Most techniques for CD34+ cell enumeration are dual platform assays. That is, they derive absolute numbers of CD34+ cells from either the flow cytometrically assessed per cent (%) CD34+ cells within the nucleated cells and/or the white blood cell count from a haematology cell analyser. Recently, so-called single-platform assays have been developed, in which the absolute number of CD34+ cells is directly derived from a single flow cytometric measurement. The present study aims to compare the variation between eight laboratories in CD34+ cell counts from paired assays of 15 samples using a common single (ProCOUNT) and the local dual-platform method. Six laboratories used the 'SIHON' and two the 'ISHAGE' protocol for CD34+ cell enumeration. Use of the single-platform method reduced the inter-laboratory variation in per cent and absolute numbers of CD34+ cells, as measured by interquartile ranges, by half but did not lead to an appreciable reduction of the inter-laboratory variation in white blood cell counts. Thus, part of the reduced inter-laboratory variation obtained with ProCOUNT may have been a result of the use of standardized procedures and reagents to detect CD34+ cells. In order to eliminate any variation arising from the use of different local protocols for percentage of CD34+ cell assessments, a comparison was made of the ProCOUNT-derived absolute CD34+ cell numbers (i.e. single platform) with the dual-platform absolute CD34+ cell numbers calculated by multiplying ProCOUNT-derived percentage of CD34+ cells and with the corresponding haematology analyser-derived white blood cell count. Regardless, the interquartile ranges of absolute CD34+ cell numbers remained almost a factor of two smaller with the use of the single platform method. Thus, these results suggest that single-platform methodology can reduce the variation in absolute CD34+ cell numbers between laboratories.