c-myb is an important transcription factor in early hematopoietic development and differentiation. In the study presented here, we asked the question whether a reduction in the level of c-myb expression led to a perturbation of the kinetics of hematopoietic development in differentiating embryonic stem cells. To this end, we induced hematopoietic differentiation of embryonic stem cells in methylcellulose medium in the absence of LIF. Hematopoietic cells formed in embryoid bodies were analyzed by methylcellulose colony assay and the pattern of gene expression was examined by real-time polymerase chain reaction. Our results show that even a small reduction of c-myb expression levels to 55% led to a significant alteration of progenitor development. Erythroid differentiation was particularly affected. However, we do not observe significant alterations in the expression of genes encoding for selected erythroid marker genes.