Expression pattern of the Xc-myb, a HLH gene, was analyzed in the early embryogenesis of Xenopus laevis. In situ hybridization by using Xc-myb cDNA as a probe demonstrated that several cell types/tissues including neural plate, somites, and hematopoietic cells express high levels of zygotic Xc-myb transcript. Such expression pattern of Xc-myb was very similar to that of the Xenopus c-myc, another HLH gene and whose protein product was known to form a heterodimer with Max to effectively activate target genes. These observation suggests that the HLH genes like myb and myc have important roles in controlling neuroblast and other types of cells determination and/or cell differentiation during the early amphibian development.