Placement of an object in three-dimensional space is a six-degree-of-freedom (6D) operation requiring three variables to specify location and three more to specify orientation. This paper reports on an investigation using a six-degree-of-freedom digitizer to manipulate 3D scenes stored in a computer. Two experiments are presented, which evaluate speed and accuracy of placement under different conditions. Results show that placement times are faster with stereopsis, when z translations are disabled (when accurate translation is required) and when both rotations and translations are allowed simultaneously. The implications of these results are discussed.