Process for converting synthesis gas to hydrocarbons which comprises contacting a gaseous stream comprising synthesis gas, at an elevated temperature and pressure, with a suspension comprising a particulate Fischer-Tropsch catalyst having a particle size in the range 5 microns to 500 microns, suspended in a liquid medium, in a system comprising at least one high shear mixing zone and a reactor vessel. The suspension and the gaseous stream is passed through the high shear mixing zone(s) wherein the gaseous stream is broken down into gas bubbles. The suspension having gas bubbles dispersed therein is discharged from the high shear mixing zone(s) into the reactor vessel, and suspension comprising the particulate Fischer-Tropsch catalyst suspended in the liquid medium and liquid hydrocarbon products is withdrawn from the reactor vessel and at least a portion of the suspension is recycled to the high shear mixing zone(s) via an external conduit at a flow rate of at least 10,000 m.sup.3 of suspension per hour. A side stream from the suspension flowing through the external conduit is taken and passed directly to a filtration unit.