Manipulating slice planes is an important task for exploring volumetric datasets. Since this task is inherently 3D, it is difficult to accomplish with standard 2D input devices. Alternative interaction techniques have been proposed for direct and natural 3D manipulation of slice planes. However, they also require bulky and dedicated hardware, making them inconvenient for everyday work. To address this issue, we adapted two of these techniques for use in a portable and self-contained handheld AR environment. The first is based on a tangible slicing tool, and the other is based on a spatially aware display. In this paper, we describe our design choices and the technical challenges encountered in this implementation. We then present the results, both objective and subjective, from an evaluation of the two slicing techniques. Our study provides new insight into the usability of these techniques in a handheld AR setting.