Neutral mucin contains aminohexose and free hexose. Acid mucin also contains aminohexose and different kinds of acid radical. Neutral mucins are found in gastric mucosa, duodenum gland, submandibular gland and prostatic epithelium. Acid mucins are found in respiratory tract, goblet cells of digestive tract, aortic wall, cartilage matrix, cornea and skin. Gastric mucosa secretes neutral mucus. Acid mucins are secreted in intestinal metaplasia of stomach or intestinal type of gastric cancer. However, gastric type of gastric cancer secretes neutral mucus. Acid and neutral mucins are hardly distinguished in hematoxylin and eosin stain. With AB-PAS stain, acid mucin can be stained blue by Alcian stain. Neutral musin can be stained red by PAS.