We have analysed β-globin mRNA sequences in total RNA extracted from embryos and tadpoles of Xenopus laevis at different stages of development and we have identified the most abundantly transcribed β-globin mRNA (βT1). The entire nucleotide sequence of a cDNA clone corresponding to this mRNA is known. We have now identified the gene corresponding to this mRNA and we have determined the nucleotide sequences of its immediate 5′-flanking region. Using a DNA fragment from within the coding region of the cloned βT1 cDNA we show, by primer extension analysis, that βT1 mRNA is first detectable at stage 28–32 of development. This is the time at which the first presumptive erythropoietic tissue, the ventral blood island, becomes observable histologically. We show that two minor β-globin genes, distinct from βT1, are expressed during early stages of development, and that their expression ceases shortly after the beginning of the feeding stage. We term these two early larval genes βE1 and βE2. A third minor β-globin gene is expressed during early development but, unlike βE1 and βE2, it is also expressed throughout subsequent larval development. We term this gene βT2 and show that it corresponds to a gene previously termed β II L. Finally, using a primer derived from the major adult β-globin gene (β1), we have analysed the accumulation of the major adult β-globin mRNA during larval development, and we show that this sequence does not accumulate to any significant level before metamorphosis.