Eighty-nine dogs with malignant oral melanoma were selected for study. All dogs were clinically staged and treated with either surgical excision alone or surgery plus C. parvum immunotherapy. There was no difference in survival time between the two treatment groups. However, in dogs with advanced disease (Stages II, III) there was a statistical difference between surgery alone versus surgery plus C. parvum (p = 0.01). Dogs with Stage I disease (tumor less than 2 cm diameter) had a statistically improved survival (p = 0.02) regardless of the therapy given. These results suggest that C. parvum, when combined with surgery, may have antitumor activity in the canine melanoma model.