The IR spectra of NH (super +) 4 -saturated smectites were examined in terms of their charge characteristics. The v 4 NH (super +) 4 band near 1440 cm (super -1) , observed in the DRIFTS spectra (obtained without use of a KBr matrix), was assigned to the vibrations of NH (super +) 4 ions compensating the negative charge of the clays. When KBr was used as a diluting matrix, the v 4 NH (super +) 4 band was located at 1400 and/or 1440 cm (super -1) . The band at 1400 cm (super -1) , related to NH 4 Br, originated from the replacement of NH (super +) 4 in the clay by K (super +) from the KBr. For swelling clay minerals this band indicates that layers have permanent low charge density and/or variable charge. For non-swelling clay minerals, the 1400 cm (super -1) band characterizes the presence of variable charges only. The v 4 NH (super +) 4 band at 1440 cm (super -1) suggests that NH (super +) 4 in the clay was not replaced by K (super +) from KBr and remains in the interlayer space of the clay minerals. This absorption is due to NH (super +) 4 compensating only permanent charge in the interlayers, or part of the interlayers with a high charge density. The presence of both bands at 1400 cm (super -1) and 1440 cm (super -1) in the IR spectrum suggests that the clays studied have a heterogeneous interlayer charge.