Abstract: A small suction pump that may be implanted in test animals to draw biological fluid samples is disclosed. The pump, before it is activated, consists of an outer, impermeable expansible housing, an inner, expanded elastomeric fluid collection container housed within the housing, a port extending from the container lumen through the housing, a rigid semipermeable partition between the housing and inner container, and a water-imbibing composition interposed between the housing and the partition. The pump is activated by charging water between the partition and container. Such charging of water forces the container to collapse. In operation water is drawn through the partition by the water imbibing composition thereby permitting the container to expand and suck fluid via the port.