A centrifugal reactor system comprises: (a) a chamber rotatable about an axis; (b) a device for rotating the chamber about the axis; (c) at least a first inlet in communicative connection with the chamber for introducing a feed contg. 1 reactant into the chamber, and (d) at least a first outlet in communicative connection with the chamber for removing liq. The chamber contains 2 liq. phases comprising a first phase and a second phase in contact with each other. The first phase comprises a catalyst system (CS) to effect a desired reaction involving 1 reactant of the feed, which reactant partitions into the first phase to contact the CS and react to produce a reaction prod., at least a portion of which partitions into the second phase. The chamber is rotated at a tangential velocity to create sufficient centrifugal force to maintain a vol. of the second phase as an unmixed phase at a location of communicative connection of the first out let with the chamber, thereby enabling removal of an amt. of the second phase from the chamber while minimising loss of the CS. Also claimed is a method for performing a catalysed reaction in a multiphase system, comprising: (a) introducing a feed contg. 1 reactant into a chamber rotatable about an axis which contains 2 liq. phases comprising a first phase and a second phase in contact with each other, the first phase comprising a CS to effect a desired reaction involving the 1 reactant of the feed, which reactant partitions into the first phase to contact the CS and react to produce prod., at least of which partitions into the second phase, (b) rotating the chamber at a tangential velocity to create sufficient centrifugal force to maintain a vol. of the second phase as a unmixed phase at a location of communicative connection of an outlet of the chamber, and (c) removing an amt. of the second phase from the chamber via the outlet.    USE -   The method is partic. useful in enzyme-catalysed reactions, e.g. the removal of organophosphate pesticides such as paraoxon, parathion and methyl paraoxon from contaminated material using phospho-tri:esterase.    ADVANTAGE -   The method can provide a multiphase reaction/sepn. of prods. or extn/sepn. in a continuous single-stage process. It provides for the removal of prods. while minimising or completely preventing loss of the CS.