Clinical testing of a commercially prepared extract of the New Zealand green-lipped mussel (Green Mussel E Kyowa, GMEK) was conducted on several different kinds of joint diseases of dogs and cats. The experimental animals were 43 dogs and 6 cats with pain and/or lameness, which were thought to be caused by joint disease. GMEK was remarkably effective in 18, effective in 21, slightly effective in 7, and ineffective in 1 case. The clinical symptom was aggravated in 2 cases. NO adverse effects were clinically observed except temporary diarrhea in 4 cases. GMEK was confirmed to be an excellent nutritional supplement for dogs and cats with joint diseases.