The technique of RNA in situ hybridization to mouse embryo sections from different developmental stages was used to perform a detailed analysis of the expression pattern of the gene for the architectural chromatin factor Hmgic. At early stages of fetal development (day 9.5 post conceptionem), Hmgic is expressed at a high rate throughout the whole embryo. In the second half of development, the pattern of expression becomes more restricted. Expression is found in mesenchymal derivatives, which differentiate into cartilage or muscle, in epithelial cell layers of the lung, pancreas, submandibular gland, and vibrissae, and in some special parts of the central nervous system. The expression pattern of Hmgic was compared with the previously reported studies of Hmgiy gene expression, another member of the Hmgic protein family, and with the expression of histone H4, Hist4, which is representative of cellular proliferation stages. In some tissues the pattern of expression for both factors coincides, but in others the expression is different. Hmgic expression correlates throughout fetal development with high proliferative activity. In contrast, Hmgiy is expressed also in tissues with no proliferative activity, such as the cortical plate of the telencephalon and the spinal cord at late gestational stages.