A method is described for shutting down a Fischer-Tropsch reactor fed with a reactant gas mixture comprising a synthesis gas and a recycle gas recovered from the Fischer-Tropsch reactor in a synthesis loop, said Fischer-Tropsch reactor containing a Fischer-Tropsch catalyst cooled indirectly by a coolant under pressure, comprising the steps of: (a) depressurising the coolant to cool the reactant gas mixture to quench Fischer-Tropsch reactions taking place in the Fischer-Tropsch reactor, (b) stopping the synthesis gas feed to the Fischer-Tropsch reactor, and (c) maintaining circulation of the recycle gas through the Fischer-Tropsch reactor during steps (a) and (b) to remove heat from the Fischer-Tropsch reactor. The method safely facilitates a more rapid return to operating conditions than a full shut-down.