Sialic acid is a component of glycoproteins that influences enzymatic and receptor functions of cells. During proliferation and differentiation of tissues, sialic acid can serve as a recognition determinant in intercellular communication and interactions of cells with the extracellular matrix. In the present study, sialic acid expression in relation to developmental maturity of the lung has been studied. We analyzed 12 necroptic lung specimens from foetuses of different gestational ages from the 15th week to the neonate. Sections were stained histochemically using 3 lectins specific for sialic acid: Tritrichomonas mobilensis lectin (TML), specific for sialic acid without linkage preference, Sambucus nigra agglutinin (SNA), specific for alpha2,6-linked sialic acid, and Maackia amurensis leucoagglutinin (MAL), specific for alpha2,3-linked sialic acid. MAL positivity dominated over SNA positivity showing prevalence of alpha2,3-linked sialic acids to be homogeneously distributed in the lung at the canalicular stage of development. In more mature lungs, well-differentiated bronchial epithelium showed strong sialic acid expression of both linkages. Sialic acid with alpha2,6 linkage dominated in vascular endothelium. Our results showed a slight decrease in sialic acid expression in lungs with gestational age to a relative minimum before birth. Lectin staining of mature lung tissue showed intense sialic acid expression in alveolar epithelial type II cells. Changes in expression of specific sialic acids during differentiation of the lungs may be useful as marker of the degree of maturity of the foetus.