The invention relates to a method and an apparatus for feeding an installation with fibres, which installation is fed with fibre tufts, the fibre tufts are opened at least partially and fed by means of a feed apparatus to a pneumatic feeding installation, which guides the fibres into the reservoir of at least one fibre-processing machine, especially a flat card, roller card, opener or cleaner.The invention is characterised in that, by means of a regulating circuit into which the actual pressure values measured and further processed in the pneumatic feeding installation are introduced, and into which the mass flow of the further processed fibres measured and further processed at at least one fibre-processing machine is introduced, the optimal operating point of the installation is determined by means of a regulating algorithm, and a signal is passed to an actuator of the feed apparatus for regulating the amount of fibre tufts.