The fact that the CD30 molecule can mediate signals for cell proliferation or apoptosis prompted us to perform a systematic investigation of CD30 antigen expression in embryonal tissues during proliferation and differentiation stages. We first targeted the foetal human intestinal cryptae cells with positive results. The epidermis is a dynamic epithelium that is constantly renewed throughout life. The basal layer, attached to the basement membrane, contains the dividing cells of the skin and as cells move up from this layer they undergo differentiation, ending in the formation of a terminally differentiated anucleate cell called squame. It is intriguing to find out if cells in the basal layer can express the CD30 antigen. We investigated the immunohistochemical expression of CD30 antigen in 15 paraffin-embedded tissue samples representing epidermis and epidermal buds from foetuses after spontaneous abortion in the 8th, 10th and 12th weeks of gestation, respectively, using the monoclonal antibody NCL-CD30. A Northern blotting analysis was additionally performed. The results showed that: (1) the epithelial cells of the epidermis in the developing skin express the CD30 antigen; (2) CD30 expression in these epithelial cells is higher in cases of hormonal administration than in normal gestation; (3) a similar positive reaction involved the epidermal buds associated with the development of the skin appendages. Northern blots of tissue sections using a CD30 cDNA probe detected mRNAs of the same molecular mass and variety similarly to those in the positive control cell line HUT 102.