Cell differentiation depends mainly on specific mRNA expression. To quantify the expression of a particular gene, the normalisation with respect to the expression of a reference gene is carried out. This is based on the assumption that the expression of the reference gene is constant during development, in different cells or tissues or after treatment. Xenopus laevis studies have frequently used eEF-1 alpha, GAPDH, ODC, L8, and H4 as reference genes. The aim of this work was to examine, by real-time RT-PCR, the expression profiles of the above-mentioned five reference genes during early development of X. laevis. It is shown that their expression profiles vary greatly during X. laevis development. The developmental changes of mRNA expression can thus significantly compromise the relative mRNA quantification based on these reference genes, when different developmental stages are to be compared. The normalisation against total RNA is recommended instead. Developmental Dynamics 235:754–758, 2006. © 2006 Wiley-Liss, Inc.