When testlet effects and item idiosyncratic features are both considered to be the reasons of DIF in educational tests using testlets (Wainer & Kiely, 1987) or item bundles (Rosenbaum, 1988), it is interesting to investigate the phenomena of DIF amplification and cancellation due to the interactive effects of these two factors. This research applies the multiple-group testlet item response theory model developed by Li "et al." (2006) to examine in detail different situations of DIF amplification and cancellation at the item and testlet level using testlet characteristic curve procedures with signed/unsigned area indices and logistic regression. (Contains 7 figures, 14 tables, and 4 footnotes.)