Galectin-1 (gal-1), a member of the mammalian beta-galactoside-binding proteins, preferentially recognizes Galbeta1-4GlcNAc (LacNAc) sequences of oligosaccharides associated with several cell surface glycoconjugates. As demonstrated histochemically, gal-1 recognizes appropriate glycoepitopes on human breast cancer cells (MCF7) and on human chorionic carcinoma cells (BeWo). Gal-1 is expressed in many malignant and normal tissues. A high level of expression is found in lymphatic organs, which feature high rates of apoptosis. Furthermore, it is known that galectin-1 can initiate T cell apoptosis. In this study, we examined the apoptotic potential of gal-1 in vitro on MCF7 and BeWo cells. After growing both cell lines on chamber-slides for three days, apoptosis was induced by incubation with 30 microg gal-1 per ml serum-free medium for 6, 9 and 20 hours. To avoid false increased rates of apoptosis by deletion of FCS, all approaches were done with and without FCS. Apoptotic cells were detected by in situ nick translation. The rate of apoptosis was determined by counting 1500 cells per chamberslide. The normal rate of apoptosis ranged between 0.1% and 0.3%. The incubation of both cell lines with 30 microg/ml gal-1 in serum-free medium for 6 and 9 hours marginally raised the number of apoptotic cells. An increase of apoptosis was only shown by additional stimuli like hyperthermia, removal of CO2 and FCS for 20 hours. Impressing findings were manifested in an older passage of BeWo cells, in which only omission of FCS caused apoptotic rates for up to 25% after 6 hours. The presence of mycoplasma in this BeWo passage was shown by PCR. Our results demonstrated, that galectin-1 shows apoptotic potential in both the epithelial tumour cell lines examined only with additional stress stimuli.