Neuraminic acids are widely expressed as terminal carbohydrates on glycoconjugates and are involved in a variety of biological functions. The key enzyme of N-acetylneuraminic acid synthesis is UDP-N-acetylglucosamine-2-epimerase/N-acetylmannosamine kinase, which catalyses the first two steps of neuraminic acid biosynthesis in the cytosol. In this study we report the complete amino acid sequence of the mouse UDP-N-acetylglucosamine-2-epimerase/N-acetylmannosamine kinase. The ORF of 2166 bp encodes 722 amino acids and a protein with a predicted molecular mass of 79.2 kDa. Northern blot analysis and in situ hybridization revealed that UDP-N-acetylglucosamine-2-epimerase/N-acetylmannosamine kinase is expressed at early stages during development and in all tissues investigated with a maximal expression in the liver.