Effects of blocking words by frequency class (high vs. low) and neighborhood density (high vs. low) were examined in two experiments using progressive demasking and lexical decision tasks. The aim was to examine the predictions of a task-specific response criteria account of list-blocking effects. Distinct patterns of blocking effects were obtained in the two tasks. In the progressive demasking task, a pure-list disadvantage was obtained to low frequency-high density words, whereas high frequency-low density produced a trend toward a pure-list advantage. In lexical decision, high-frequency words showed a pure-list advantage that was strongest in high-density words, whereas low frequency-low density words produced a trend toward a pure-list disadvantage. A simulation study implementing task-specific response criteria within the framework of the multiple read-out model provided an accurate description of the blocking effects obtained in the experiments. It is argued that adjustments of task-specific response criteria determine changes in list-blocking effects across different tasks.