In this paper we study case of the Lagrangians affine in first derivatives in first order field theory (for example Dirac field Lagrangian is of this type). By the regularization procedure we mean the process how to find appropriate Lepagean equivalent for given Lagrangian (in the sense of the geometric meaning of the regularity). The theory is illustrated od an example in dimension 4. The relations to multisymplectic forms are discussed.