Abstract: The present invention relates to a method for reducing the spreading of additional agent(s) which is/are introduced into the process at a papermaking machine. A flowable paper pulp including fibres and a process liquid and having a consistency of not more than 10% is conducted towards the paper machine's headbox (5). Prior to the introduction (14) of said additional agent the consistency of the pulp is increased to a value higher than 10% by removing (8) process liquid and conducting (11) it in the upstream direction, while compensating process liquid is introduced (13) downstream. The present invention also relates to an arrangement at a paper machine, where separating means (8) are arranged in the process direction before means (14) for introducing additional agent (s).