Reported here are Stark-effect measurements of the permanent electric dipole moments of two structural isomers of aminobenzonitrile, 2ABN and 3ABN, using high-resolution laser molecular beam techniques. When combined with previous results on 4ABN, the data show that each structural isomer has a unique dipole moment, in both its-round (S-0) and electronically excited (S-1) states. thereby providing a means of distinguishing them. Possible applications of the method to other, biologically relevant molecules are discussed.