This paper proposes a new field of user interfaces called multi-computer direct manipulation and presents a pen-based direct manipulation technique that can be used for data transfer between different computers as well as within the same computer. The proposed Pick-and-Drop allows a user to pick up an object on a display and drop it on another display as if he/she were manipulating a physical object. Even though the pen itself does not have storage capabilities, a combination of Pen-ID and the pen manager on the network provides the illusion that the pen can physically pick up and move a computer object. Based on this concept, we have built several experimental applications using palm-sized, desktop, and wall-sized pen computers. We also considered the importance of physical artifacts in designing user interfaces in a future computing environment.