The androgen receptor (AR) is unusual among nuclear receptors in that most of its activity is mediated via the constitutive activation functionAF1 in the amino-terminal domain, whereas the ligand-dependent AF2 in the ligand-binding domain appears to be very weak. Most coactivators interact with AF2 of many nuclear receptors via conserved, helical LxxLL motifs (where L stands for leucine and x for any amino acid). Although AF2 of the AR is very weak, we demonstrated ligand-dependent activity that can be potentiated by interaction with the LxxLL motifs. We characterizeda second, ligand-independent recruitment of SRC1 to AF1 of the AR. Thisinvolves at least two amino acid motifs located within a glutamine-richdomain. Mutation analysis of the p160s showed that the relative contribution of the two recruitment mechanisms, via the LxxLL motifs or via theglutamine-rich region depend on the nature of the enhancers tested. However, in case of the AR, the AF1-coactivator interaction is functionallythe more important. Our results could lead to the development of new therapeutic treatments for prostate cancer. Since there is growing evidence that the AR and its cofactors may be implicated in the progression of hormone-dependent to hormone-independent prostate cancer, novel targets could include the interaction of the AR with coactivators. We suggest that AR coactivator antagonists, based on the glutamine-rich region of thecoactivator, could inhibit AR activity, even in AR-positive hormone refractory prostate cancer.Endocrine disrupters pose a growing threat to human and wildlife health. Validated test systems are required to study the mechanisms by which chemicals possibly interfere with the endocrine system. As a preliminary experiment to identify compounds with (anti)androgenic activity, we developed several in vitro bioassays, based on different AR functions, like AR transactivation and interaction between the amino-terminaldomain and the ligand-binding domain. The full-length AR assay, based on activation of the transcription of an androgen-responsive reporter gene in the presence of androgen, proved to excel in terms of high fold induction range and low minimal detection limit. The bioassay has been proven to be useful to study androgenic and anti-androgenic potencies of environmental water samples and also to investigate possible endocrine disrupting effects of some pesticides and polychlorinated biphenyls (PCBs).