The invention relates to a method for start-up and operation of a Fischer-Tropsch reactor comprising the steps of: (a) providing a reactor with a fixed bed of reduced Fischer-Tropsch catalyst that comprises cobalt as catalytically active metal; (b) supplying a gaseous feed stream comprising carbon monoxide and hydrogen to the reactor, wherein the gaseous feed stream comprises a nitrogen-containing compound other than molecular nitrogen in an initial concentration, wherein the initial concentration in the range of from 10 to 350 ppbv based on the volume of the gaseous feed stream; (c) converting carbon monoxide and hydrogen supplied with the gaseous feed stream to the reactor into hydrocarbons at a reaction temperature and at a set reactor productivity, whilst maintaining the initial concentration of the nitrogen-containing compound and maintaining the set reactor productivity during a first time period by adjusting the reaction temperature; (d) decreasing the concentration of the nitrogen- containing compound to a second concentration in the range of from 0 to 20 ppbv, wherein the second concentration is at least 5 ppbv below the initial concentration, preferably at least 20 ppbv below the initial concentration, and maintaining the reactor productivity by adjusting the reaction temperature.