Method of and apparatus for controlling the temperature of a fluidized bed reactor (10), comprising separator means (16) for separating first solid particles from the fluidized bed reactor; a return duct (30) for returning a first portion of the first solid particles to the fluidized bed reactor; a discharge duct (50) for the discharge of a second portion of the first solid particles and an inletduct (52) for transferring second solid particles from a second fluidized bed reactor to said fluidized bed reactor, in which the return duct (30) and the inlet duct (52) share a common end 10 portion (54) for transferring a mixture of solid particles, formed of the first portion of the first solid particles and the second solid particles, to the fluidized bed reactor (10). Said apparatus also preferably comprises a fluidized mixing device (58) for mixing the first portion of the solid particles and the second solid particles with each other.