Transfected muscle can be used as a secreting tissue for therapeutic proteins. Skeletal muscle transfection is increased by suitable electric pulse application (electrotransfer). We and others had shown that electrotransfer of interleukin-10 encoding plasmid is an effective strategy in animal models of chronic diseases such as myocarditis, atherosclerosis, or rheumatoid arthritis. In the present work, we have studied murine interleukin-10 production and secretion after i.m. electrotransfer. In immunocompetent mice, serum and muscle mIL-10 levels were enhanced by electrotransfer. Serum mIL-10 concentration reached rapidly a peak level 2 days after electrotransfer. It then decreased to background at day 14. Muscle mIL-10 mRNA and protein remained more stable, being detectable up to 84 days after electrotransfer. A boost reinjection led to similar high level of circulating mIL-10. The fast decrease of serum mIL-10 was not observed in SCID mice.