['Hemophilia A treatment relies on costly factor VIII (FVIII) replacement that may transmit iatrogenic viral diseases. Viral vectors and cell implants are being developed as improvements. We investigated in vivo electroporation of naked DNA as a safe and simple method for correcting FVIII deficiency.', 'B-domain-deleted murine FVIII cDNA expression plasmids were constructed with CMV and elongation factor 1alpha promoters for characterisation in murine C2C12 myoblasts. The construct conferring highest in vitro FVIII secretion was electroporated into skeletal muscle of FVII null mice in vivo for phenotypic correction using a protocol that minimised tissue injury.', 'B-domain-deleted murine FVIII cDNA plasmids induced FVIII secretion from stably transfected C2C12 myoblasts (0.54+/-0.20 mU/day/10(5) cells). Phenotypic correction of hemophilic mice was more consistently achieved using a protocol for in vivo electroporation of gastrocnemius muscle with FVIII cDNA that reduced tissue injury by the use of plate electrodes, hyaluronidase pre-treatment and lower field strength. This technique was associated with <10% muscle necrosis. Activated partial thromboplastin time decreased from 51.4+/-3.3 to 34.7+/-1.1 (mean+/-s.e.m.) seconds (p=0.0004) following in vivo electroporation (0.1 mg plasmid/limb; 8x20 ms pulses, 175 V/cm, 1 Hz) of hemophilic mice. All hemophilic mice (8/8) survived hemostatic challenge after muscle electroporation with FVIII cDNA, whereas all (9/9) untreated hemophilic mice died. Plasmid DNA was detectable only in electroporated muscle and not in all other organs tested, including gonads.'] Does fVIII gene delivery by muscle electroporation correct murine hemophilia A?