The effects of worry and rumination on affective states and mentation type were examined in an unselected undergraduate sample in Study 1 and in a sample of individuals with high trait worry and rumination, high rumination, and low worry/rumination in Study 2. Participants engaged in worry and rumination inductions, counterbalanced in order across participants to assess main and interactive effects of these types of negative thinking. During mentation periods, the thought vs. imaginal nature and the temporal orientation of mentations were assessed 5 times. Following mentation periods, negative and positive affect, relaxation, anxiety, and depression were assessed. Both worry and rumination produced increases in negative affect and decreases in positive affect. Worry tended to generate greater anxiety, and rumination tended to generate greater depression. Interactive effects were also found indicating that worry may lessen the anxiety experienced during subsequent rumination. Moreover, worry lessened the depressing effects of rumination. Worry was associated with significantly greater thought than imagery, compared to rumination. Rumination involved a progression from mentation about the past to mentation about the future over time. Implications for understanding the generation of negative affect and comorbid anxiety and depression are discussed.