Seal for sealing against fluids 1 comprising a pair of elements 2, 3 intended to fit between two machine parts 13, 14 which can move with respect to one another, a first 2 of the elements including a continuous elastic ring formed of a relatively flexible material forming a spring, and a second 3 of the elements comprising a continuous annular seal body housing the first element 2, the second body 3 being formed of synthetic resins and having a substantially U-shaped cross-section and comprising a pair of annular guide elements 7 fitted on the axially-opposite sides of the second element 3.