Is your dog suffering from diarrhea? Don't take it lightly. It can be dangerous. Diarrhea in dogs is not uncommon and demands concern but not necessarily alarm. One of the more common agents causing diarrhea in dogs is intestinal parasites such as roundworms, hookworms and coccidia. The latter two tend to cause a dark or bloody stool. Appropriate diagnosis is required in such a case. Also take care of his diet.