In a multi-station reaction apparatus (1) comprising an annular heat transfer block (30) formed with a plurality of cavities (31) for receiving respective reaction vessels (36), the upper surface of the heat transfer block (30) has a central recess (32) around which the said plurality of cavities (31) are arrayed. The apparatus further comprises a removable cooling module (4), the central recess (32) of the heat transfer block (30) being shaped so as to accommodate the removable cooling module (4) and corresponding surfaces of the central recess (32) of the heat transfer block (30) and the cooling module (4) being shaped such that there is a stepped interface between them. The cooling module (4) comprises a metal block having channels therein through which coolant circulates when the cooling module (4) is in use. The apparatus further comprises refluxing means (5) which are positioned above the heat transfer block (30) and arrayed annularly around a central hole (52), whereby the cooling module (4) can be inserted or removed from the heat, transfer block (30) through the hole (52) without disturbance or removal of the said reaction vessels (36) or refluxing means (5). In an alternative embodiment, the cooling module may be annular with a central recess for receiving the heat transfer block.