Regions of HIV-1 genome, encoding the V3 gp120 region, were sequenced in materials that were sampled from persons belonging to the category of individuals infected from a single source during the Rostov-Elista outbreak. The samples were obtained in 1991-1992 (10 pieces) and in 2000-2001 (16 pieces), which amounts to 8% and 13%, respectively, of a total number of patients infected by the beginning of 1990. It was established that the level of the population variability of amino-acid sequences in region V3 amounted, in 1991-1992, to 5.2% and increased to 9.1% in the samples of 2000-2001. A comparison of amino-acid sequences in region V3 from the collections of 1991-1992 and of 2000-2001 revealed the below amino-acid substitutions: from Ser13 to His, from Ley14 to Phe, from Phe to Ley and from Ley to Ala. An analysis of V3 B-epitope showed that the basic trend of its evolution consists in reciprocal transitions of L to F in position 14 and of F to L in position 20. Such substitutions ensure further changes at the "top" of the V3-loop from GPG to APG.