A self-contained fluid-cooled electro-optical plug in type module capable of being exchangeably mounted in an external chassis incorporates electronic or electro-optical devices mounted on one or more interposers which provide electrical power and electric and optical signal connections to the devices and are also provided with fluid conduits through which a cooling fluid is circulated in a closed-loop cooling path to a heat exchanger for transferring the heat generated in the devices to external heat disposal equipment in the mounting chassis.