A valve for medical instruments having a canal configured in a medical instrument and serving as input for at least one additional medical instrument is insulated from a distal-end fluid, whereby the valve housing wherein at least one fluid opening is configured, and positioned in the housing at least one insulating body can be inserted at least partly into the canal. The invention has at least one fluid opening configured in the valve housing by which the fluid can be conducted to the outside of the insulating body such that the fluid opening is so configured that the distal-side fluid can be guided out of the canal to the outside of the insulating body in such a way that the distal-side fluid reshapes the insulating body inward, insulating it, to be essentially perpendicular to the longitudinal direction of the insulating body.
