Protein-protein interactions of the p24 (HIV-1) capsid protein play an essential role in the production of infectious virus particles. To map the putative p24 dimerization site, a set of overlapping peptides spanning the p24 sequence was prepared using spot synthesis on a cellulose membrane and probed with recombinant p24 (rp24). Three sequence regions interacting with rp24 were identified. Peptides from each region were synthesized, but only one peptide was effectively able to inhibit rp24 dimerization in solution. Amino acids that were exposed in the corresponding p24 region were mutated in rp24, resulting in a significant decrease of rp24 dimerization. Thus, participation of this region in virus capsid assembly can be assumed.