The interaction between the human head and handset antennas needs to be taken into account, since mobile phones have to be functional, and, at the same time, guarantee biological compatibility. The present research analyzed the performance of several handset antennas with different slotted ground planes in free space and also in the presence of the human head. The main objective was to compare the measured bandwidth and efficiency in both environments (free space and human interaction), and the impact on the measured SAR (Specific Absorption Rate) of such antennas as functions of the slot configuration in the ground plane and the antenna's location. Results showed that slots may be useful for increasing bandwidth and efficiency while keeping similar SAR values compared to the non-slotted ground plane. Changing the antenna's location was a good way to achieve a significant SAR reduction. In some cases, when the antenna was at the lower edge of the ground plane (down position), the SAR could be reduced by a factor of two. Impedance, efficiency, and radiation patterns were measured and analyzed with a phantom head in order to understand the human head's effect on the antenna's performance. Although all antennas suffered from changes, shorted-end slots were more robust for human interaction than open-ended slots.