<p>How quickly we attend to objects plays an important role in navigating the world, especially in dynamic and rapidly changing environments. Measuring individual differences in attention speed is therefore an important, yet challenging, task. Although reaction times in visual search tasks have often been used as an intuitive proxy of such individual differences, these measures are limited by inconsistent levels of reliability and contamination by non-attentional factors. This study introduces the rate of post-target distractor intrusions (DI) in the rapid serial visual presentation (RSVP) paradigm as an alternative method of studying individual differences in the speed of attention. In RSVP, a target is presented for a brief duration and embedded among multiple distractors. DIs are reports of a subsequent distractor rather than the target and have previously been shown to be associated with the speed of attention. The present study explored the reliability and validity of DI rates as a measure of individual differences. In three studies, DI rates showed high internal consistency and test–retest reliability over a year (&gt;.90), even with a short task administration of only about 5&#xa0;minutes. Moreover, DI rates were associated with measures related to attention speed, but not with unrelated measures of attentional control, reading speed, and attentional blink effects. Taken together, DI rates can serve as a useful tool for research into individual differences in the speed of attention. Links to a downloadable and easily executable DI experiment, as well as a brief discussion of methodological considerations, are provided to facilitate such future research.</p>