Human apolipoprotein A-I gene (apoA-I) plasmid expression vectors were transferred into mice by hydrodynamic injections into tail vein. Two types of expression vectors were used. First one - pCMVcapoAI contains cDNA of apo A-I driven by human cytomegalovirus early gene promoter (CMV). Second one - pAIg contains genomic locus of intron-containing apo A-I under control of own extended 5′-regulatory region (APOAI). Hydrodynamic intravenous injections of both expression vectors led to appearance of human apo A-I mRNA in the liver and human Apo A-I protein in the serum of injected mice. Dynamics of human Apo A-I content in the serum of mice injected by pCMVcapoAI and pAIg were different. When pCMVcapoAI was used, maximal concentration of human Apo A-I protein in the mouse serum was detected one day after injection with following decline to zero level during next two weeks. Under the same conditions injections of pAIg led to maximal level of human Apo A-I concentration in the mouse serum (up to 20 mkg/ml in some animals) on the 5 ^th-7 ^th day of experiment with following graduate decline during several months (human Apo A-I concentration in the serum of oldest analyzed mouse (6 months after injection) was about 25% of its maximal level in the same animal). Levels of human Apo A-I concentration in the mouse serum were compatible after injections of both expression vectors, in spite of much more strong activity of CMV promoter in comparison with APOAI in cultured human hepatoma cells HepG2. We ascribe the revealed difference in dynamics of human Apo A-I expression to delay of apo A-I transcription from pAIg vector, that was confirmed by nested RT-PCR. Significant level and long-term persistence of human Apo A-I in the serum of mice injected by pAIg could be explained by properties of APOAI or (and) exon-intron structure of genomic apo A-I gene. To test the role of APOAI in long-term expression of human Apo A-I in the mice we performed hydrodynamic injections of plasmid vectors containing cDNA of reporter gene encoding luciferase driven by variants of APOAI. No long-term expression of luciferase was found in the livers of injected mice. Therefore, our data suggest the role of exon-intron structure in maintaining of efficient and long-term expression of transferred human apo A-I.