  In this paper we consider mappings of jet spaces that preserve the module of
canonical Pfaffian forms, but are not generally invertible. These mappings are
called contact. A lemma on the prolongation of contact mappings is proved.
Conditions are found for which mappings transform solutions of some partial
differential equations into ones of other equations. Examples of contact
mappings of differential equations are given. We consider contact mappings
depending on a parameter and give example of differential equation invariant
under the maps.
