Properties of the Dirac-Born-Infeld Lagrangian analogous to those of the Na
mbu-Goto string are analysed. In particular the Lagrangian is shown to be c
onstant or zero on the space of solutions of the equations of motion if the
Lagrangian is taken to any power other than 1/2. (C) 1999 Published by Els
evier Science B.V. All rights reserved.