Recent results from seafloor exploration and crustal drilling are used to constrain the structures within which hydrothermal circulation occurs at mid-ocean ridges (MOR). This hydrothermal activity is modeled numerically using a two-dimensional triangular domain representing the extrusive layers. The configuration is heated both at an impermeable base and along the intrusion axis. The structure is characterized by dips of a few degrees towards the axis and permeability anisotropy (Δ=Kz/Kx). The temperature fields are computed for different hydrothermal regimes defined by variable axial heat flow values characterized by variable Rayleigh numbers (Ra*). These computed temperatures are compared to those deduced from basalt alteration mineralogy observed in seafloor samples and drillcores. The mean temperature of discharge zones is considered as limited to values between 60¿ and 100 ¿C. In the isotropic case, the chosen geometry and boundary conditions are found to stabilize the convective process which advocates against a time-fluctuating behavior as a steady state is reached in an average time of 5000 years up to Ra* values as large as 600. However, Ra* values are unlikely to exceed 400, or to be smaller than 100 due to the mineralogical constraints. With Ra* larger than 100 and Δ=1, a mean temperature of 25 ¿C, compatible with celadonite-nontronite and iron-hydroxides mineralization, is obtained for the recharge zones. For a given axial heat flow and a similar permeability contrast, larger temperatures are obtained in subhorizontal settings than in subvertical ones. Small changes of permeability anisotropy are confirmed to induce large variations in temperatures and strength of the flow. ¿ American Geophysical Union 1996