The ectopic expression of a sheep growth hormone-releasing hormone (GHRH) from muscle tissues, using a myogenic plasmid expression vector pM-GHRH, has been shown to result in enhanced animal growth. Animal injected with pM-GHRH alone exhibited a daily weight gain rate of 0.84+/-0.02%/d (p < 0.05), while that of the control animal was only 0.73+/-0.04%/d. A more significant growth enhancement was observed in the group treated with pM-GHRH plus 0.25% bupivacaine. The animal displayed a daily weight gain rate of 0.87+/-0.03%/d (p<0.01). In addition, the group treated by pM-GHRH and bupivacaine had higher levels of growth hormone (GH) in their blood (1.18+/-0.33 ng/mL) compared with the group treated by pM-GHRH vector alone (p < 0.05). Evaluation of body composition by dissection and histochemical analysis indicated a significant increase in bulk with no organomegaly or associated pathology. PCR analysis demonstrated that there was little plasmid residue detected in the pM-GHRH treated sheep.