FMR technique has been shown to be capable of detecting chemical inhomogeneities present in some amorphous GdCo films. A group of bulk modes observed when the polarizing field is perpendicular to the film plane, have been shown to correspond to absorption from regions which differ slightly in their magnetization and hence in their relative Gd or Co concentration. Such inhomogeneities seem to increase with the bias voltage. A typical result shows that Gd concentration variation is in the range 1–2 at.&percent; and which is beyond any chemical analysis used currently. These inhomogeneities increase with the bias voltage and are distributed, as it were, in the whole volume of the film in a random manner as shown by acid etching experiments. Vacuum annealing at T up to 290°C does not lead to any homogenization and argon anneal leads to a new situation with a very large in plane anisotropy besides a spin wave spectra now appears in all the samples.