Diseases are one hazard that can deplete an adventurer's abilities and leave him weak and damaged. When a character first comes into contact with a disease he makes a Fortitude saving throw. If this is successful then the disease is resisted, otherwise it begins to incubate within the character. After a specified number of game hours or the character's next rest, the disease will manifest itself is the form of ability damage. Each time the character rests after the incubation period they are required to make a Fortitude saving throw to resist further ability score damage. If the character successfully makes two of these saving throws in a row, the disease is removed. Ability damage incurred from disease heals while resting. Certain diseases have special carrier effects, such as blindness or other, nastier surprises that can be applied after the incubation period ends or after 24 game hours have passed.