Question: Achievement of site-specificity and potent gene transfer is a great therapeutic challenge. Here we investigated whether intravascular application of lentiviruses (LVs) coupled to magnetic microbubbles (MMBs) could efficiently establish a localised gene transfer in vivo. As a technique for tissue specific targeting the efficiency of a combination of trapping the MMBs by localized magnetic field (MF) application and their subsequent destruction by ultrasound (US) exposure in the mouse dorsal skin fold chamber model was tested. Methods: Coupling of LVs containing a membrane GFP-fusion protein to MMBs was verified by flow cytometry. Mice (C57BL/6) were anesthetized with intraperitoneal injection of 3mg/kg body weight Midazolam, 0.03mg/kg body weight Fentanyl and 0.3mg/kg body weight Medetomidinhydrochloride in 0.9 % NaCl. In vivo, LV-coupled MMBs (1.6×106-1.5×107 infectious particles) were targeted to vessels of the mouse dorsal skin after intra-arterial injection by combined MF (1T) and US exposure (1MHz, 2W/cm2, DC50%, 30sec). Reporter gene expression (GFP) in the dorsal skin and in organs not exposed to MF and US was assessed by real-time PCR in tissue homogenates obtained 48-96h after treatment. Biodistribution of MNPs, to assess time of tissue clearance, was measured in homogenized organs by magnetic particle spectrometry 1h and 96h after injection of MMBs. Residual viral particle amount in blood, urine, stool and saliva 48-96h after treatment was analyzed with p24 ELISA and cell culture. Results: LVs readily associated with MMB in vitro (20-fold increase in fluorescent units, p<0.05, ANOVA, n=3). In vivo, MMB specifically delivered the coupled genetic material to the dorsal skin after MF and US application. The achieved gene transfer efficiency of LV-associated MMB in the dorsal skin was enhanced 120-fold compared to pDNA-associated MMB, as assessed by reporter gene expression (p<0.05, t-test, LV n=4; pDNA n=10). MNP accumulation was detected mainly in the lung and liver (19±4% and 41±9% of administered dose respectively, n=5) 1h after treatment, which was strongly reduced 96h after treatment (0.2±0.07% and 0.3±0.09% of administered dose respectively, n=4). No residual LVs were detected in the collected biological samples 48-72h after LV-MMB application (n=3). Conclusion: Magnetically-guided microbubbles were successfully applied as carriers for lentiviral gene vectors. Using the combination of magnetic targeting and US induced MB destruction, they allow for highly efficient and site-specific vascular gene transfer. Moreover, our data provides evidence that the coupled magnetic nanoparticles are effectively cleared from the organism indicating the aptitude of our method as a biocompatible therapy approach. In conclusion, the LV-associated MMB technology may represent a valuable tool for vascular gene therapy.