Vpr, one of the accessory gene products of the human immunodeficiency virus-1 (HIV-1) genome, exhibits diverse biological characteristics. Vpr functions as a transcriptional activator of HIV and heterologous promoters. It is capable of arresting cells in cell cycle progression and plays a crucial role in the infection of macrophages. Despite the wealth of information available on the biological aspects of Vpr, the structure of Vpr remains poorly understood. To gain insight into the structure-function relationship of Vpr, peptides corresponding to putative helical regions of Vpr were synthesized and their structures determined by circular dichroism (CD) spectroscopy. The CD studies confirmed the predicted helical structures of these peptides. Based on the data, a hypothetical model for the structure of Vpr was proposed which displays an anti-parallel alpha-helix core structure reminiscent of a helix-loop-helix motif. These findings are consistent with the results from mutational studies of Vpr and provide a plausible structural basis to further investigate the multiple functions of Vpr as a viral protein.