The microstructure, morphology and magnetoresistive properties of as-deposited and annealed at 700K discontinuous films of ferromagnetic metals and their alloys are investigated. It is established that the isotropic field dependences stemming from the spin-dependent electron tunneling between ferromagnetic islands are observed for as-deposited Co films with an effective thickness (d) of dCo = 5-25 nm as well as for Fe films (dFe = 10-30 nm). It is shown that the maximum values of the isotropic magnetoresistance take place in the case when the size of the islands is equal to 3-5nm and the width of the dielectric barrier between them is 1-3nm. The maximum TMR values for the films annealed at 700 K are obtained when the dielectric barrier is 2-5 nm wide.