Embryonic stem cells are a useful model to study embryonic cell attributes like pluripotency and totipotency and their molecular and cellular determinants in vitro. Embryonic stem cells can be cultivated as spontaneously differentiation embryoid bodies (EB). EBs are spherical three dimensional cell aggregates and many aspects of the lineage-specific differentiation programs observed within EBs reflect those found in the early preimplantation embryo. In order to characterise the development and differentiation (i) the GLUT isoform expression was investigated in the embryonic stem cell line D3 (ii) the influence of 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD) was studied in the embryonic carcinoma cell line (ECC) P19. Whereas the GLUT expression as a cell specific marker is well characterised in adult tissues, the expression during cell differentiation processes is still not clear. The GLUT-expression was investigated in mouse embryonic stem cell line D3 (ESC) and during spontaneous, neuronal and myogenic differentiation of EBs using RT-PCR, Western blotting and immunofluorescence. Both ESC and EBs expressed GLUT1, 3 and 8. GLUT2 and 4 were detectable in EBs starting at 15 and 2 days of culture, respectively. GLUT4 is expressed in most of differentiated stage specific embryonic antigen-1 (SSEA-1) negative cells. These data suggest, that during EB differentiation the cell-type specific GLUT expression is similar to the expression pattern in the early embryo. For determination of the TCDD influence, the cardiac muscle differentiation of P19-ECC was investigated by real time PCR, Western blotting and immunofluorescence. During differentiation alpha cardiac actin (α-MHC) mRNA was increased until day 5+5, whereas the mRNA of an important neuronal transcription factor Mash-1 was decreased by TCDD, indicating that TCDD influences the cardiomyogenic and neuronal differentiation. The amount of GLUT1, 3, 4 and 8 transcripts showed no significant TCDD effect, indicating that TCDD acts mainly on GLUT protein level and localisation. The protein amount of GLUT1 and 3 was significantly decreased during myogenic differentiation. In undifferentiated TCDD treated P19-ECC GLUT1 localisation changed from plasma membrane into cytoplasm. The glucose uptake in 5d EBs was significantly decreased. These data suggest, that TCDD influences glucose metabolism in undifferentiated and differentiating embryonic cells by affecting expression and localisation of GLUT isoforms.