Six healthy horses were selected for this study. Each subject was fitted with special front shoes designed to produce focal sole pressure to induce lameness. Focal compression was induced by tightening one screw on the left side of the left front shoe until a lameness score of 2-3 was attained. Each horse received three different treatments, with a one-week washout period between each treatment. The three treatments each horse received were: electro-acupuncture (EA) connecting acupoints Bai-hui to Duan-xue, left SI-9 to San-yang-luo, and left Qian-chan-wan to Qian-jiu for 45 minutes (80-120 Hz), a nerve block of the lateral palmar nerve (positive control to block where the screw was compressing) and sham nerve block (negative control). Lameness was evaluated by 2 separate investigators using a standardized lameness scale prior to lameness induction, after lameness was induced and after each treatment. One of the investigators evaluated only videos of the lameness examination and was blinded to treatment group. Plasma concentration of β-endorphin, cortisol and ACTH was measured before and after the 3 treatments. EA decreased the lameness score and reduced the degree of lameness significantly (P<0.001). EA also significantly increased plasma β- endorphin concentrations and reduced cortisol levels compared to the other groups, but had no effect on ACTH levels. These results suggest the release of β-endorphin may be one of the mechanisms by which acupuncture relieves pain. The results of this study further support the use of EA to treat naturally occurring lameness from hoof disease in horses.