The development, growth and survival of eukaryotic organisms require the proper regulation of tens of thousands of genes. Therefore, a correct temporal and spatial expression of genes is crucial. These expression patterns are controlled by a wide variety of mechanisms, but a major level of gene expression occurs at the transcription initiation process. In this part, the basic mechanisms of eukaryotic gene transcription will be discussed. Contents include: 1) General Introduction, 2) Characterization of the two coactivator interacting surfaces of the androgen receptor and their relative role in transcriptional control, 3) Screening for environmental (anti)androgenic activity, 4) Detection of endocrine disrupting activities in pesticides and polychlorinated biphenyls, and 5) General Discussion / Future Perspectives.