Abstract: An apparatus and method for on-line testing for the presence of an endotoxin within a fluid sample from a fluid line. The apparatus is positioned in fluid communication with a fluid line to perform the on-line fluid testing for the presence of at least one endotoxin. The apparatus can include a housing and a fluid sampling system positioned in fluid communication with the fluid line. The fluid sampling system can comprise a valve for controlling the fluid flow from the fluid line into the fluid sampling system. A fluid flow well is positioned within the housing and in fluid communication with the fluid sampling system. A removable assembly can also be secured within the housing. The removable assembly comprises a plurality of wells for receiving used and unused fluid carrying members that can receive samples from the fluid flow well, a plurality of fluid sample receiving wells, and a plurality of vessel retention positions comprising recesses for securely receiving portions of respective fluid vessels.