The androgen receptor (AR) belongs to the nuclear receptor super-family and is of particular importance for the mediation of the androgen signal. Recently, sequencing of the AR has been performed in some teleost fish. Until now, in the rainbow trout (Takeo et al. 1999) and the Japanese eel (Todo et al. 1999; Ikeuchi et al. 1999) two distinct AR sequences have been characterised. In these species, the DNA-binding domain and the ligand-binding domain are highly con- served (respectively until 90% and 70% of identity with the same domain of mammalians ARs) (Touhata 1999). However some very divergent forms have been described in two teleost fish: in Astatotilapia burtoni (AF121257) and in Oreochromis niloticus (AB045211). These results lead us to suppose the existence of a second type of AR in fish. In order to reconstruct the evolution of ARs, characterised AR forms that are present in teleost and non-teleost fish