In an exhaust gas turbocharger turbine for an internal combustion engine including a turbine housing with a turbine wheel disposed therein, an axially movable slide member having a front end with a vane structure is disposed in an annular gap formed in the turbine housing adjacent a radial flow passage leading to the turbine wheel such that the annular slide member is movable between a first position in which its vane structure is disposed in the radial flow passage and a second position in which the vane structure is received within the annular gap and blow off passages which extend through the turbine housing from the radial flow passage through the annular gap to the discharge side of the turbine are opened when the annular slide member is further retracted for discharging gas from the radial flow passage to the turbine discharge side while by-passing the turbine.