The secondary relaxations in amorphous ethyl cellulose are studied using thermally stimulated depolarization currents (TSDCs) in the temperature region from 165 degrees C (108 K) up to 145 degrees C (418 K). The influence of aging on the current peaks of the secondary relaxation is discussed, and it is concluded that some modes of motion of this mobility are aging independent, while others are affected by aging. A particular attention is focused on the discussion of the degree of co-operativity of the motional modes of the secondary relaxation. The conclusion to be driven from the obtained TSDC results is that the aging-independent motional modes, as well as those that are aging dependent, do not show any appreciable co-operative character. (C) 2009 Wiley Perodicals, Inc. J Polym Sci Par-t B: Polym Phys 47: 820-829, 2009