the invention pertains to an apparatus for premixing additives and feeding them into a polymer melt stream . the apparatus has a conducting element 2 , first and a second intermediate element 4 a and 4 b , and a pump assembly 6 , wherein the polymer melt stream is guided through channels 8 and 10 of the conducting element . the second intermediate element 4 a has a feed element 12 that extends into the first channel 8 to form a ring channel . the feed element 12 is surrounded by openings 14 , through which a portion of the polymer melt is drawn off , so that it can be mixed with an additive inside the pump assembly 6 . this mixture is then returned via the feed element 12 to the polymer melt stream . the apparatus according to the invention makes it possible to decrease the residence times of the polymer and requires very little in the way of apparatus .