A. Cartoon for in vivo plasmid delivery and electroporation for the lungs showing endotracheal tube and electrodes. B. Dose-dependent gene transfer and expression in vivo. Five hundred microliters of DNA or saline was delivered to the lungs of anesthetized animals at the indicated doses, followed by electroporation (200 V/cm; 8 pulses; 10 μsec each). Three days later, luciferase gene expression was measured (mean ± sem, n=6). *, p < 0.01 and #, p < 0.001 versus no DNA using the non-parametric Mann-Whitney U-test. C. Effects of pulse length on in vivo gene transfer. One hundred micrograms of plasmid was delivered to the lungs of anesthetized rats which were immediately electroporated at 200 V/cm using 8 pulses at 10 μsec or 1 msec or at 100 V/cm using 8 pulses at 10 msec. Three days later luciferase expression was measured (mean ± sem, n=6). *, p < 0.01 compared to DNA only (0 msec) by Mann-Whitney U-test.