We describe a simple cell isolation device that allows the separation and sequential collection of fat cells as they are released from adipose tissue fragments exposed to a collagenase preparation. This is done without interrupting the digestion process. Use of the device allows for appreciable lowering of the degree of cell damage and the extent to which larger cells are ruptured during the isolation process. Fat cells isolated by this technique elicit a higher level of metabolic activity as reflected by their improved response to the lipolytic action of epinephrine.