The day-to-day instrument detection but automatic compensations were stable. Manual compensation settings were satisfactory using available facilities. Commercial and UK NEQAS quality control results were acceptable. The intra-experiment reproducibility was good (coefficient of variation (CV) <3%) but highly operator-dependant (CD4+ T cell count CVs from 1.2 to 9.7, six operators). Storage of samples was acceptable, but storage of stained samples altered absolute count reliability. Serial dilutions show a good count accuracy. The FACScanto T subsets and B cell data were highly correlated with our reference values (r2 > 0.87) and absolutes values were very close (slopes > 0.89). The gating strategy, fluorochrome choice, and compensation setting are discussed. A few improvements are expected (sample loader, data management, auto-gating, acquisition parameters, sample mixing, absolute values calculation, etc). In conclusions, despite its complexity, 6 color staining is a reliable, stable, and highly informative technique for lymphocyte subset monitoring but remains to be optimized.