The effect of instructions on basic cognitive tasks was investigated. In the first study, 60 college students completed both a choice reaction time and a modified match-to-sample task. Students were given either written, non-verbal, or no instructions. Mean level of performance changed across type of instruction for each task. The correlations between the task parameters and a measure of general intelligence also appeared to change across instructional conditions. A second study was conducted with 464 Air Force and National Guard recruits who completed choice reaction time, match-to-sample, tachistoscopic threshold, and probed recall tasks. Approximately half of these subjects received standard written instructions while the others received no instructions. Mean group differences were substantial but decreased with practice. Patterns of individual differences between the instruction and no-instruction conditions varied more with increased task complexity, with greater change occurring in more complex tasks such as probed recall. In sum, instructions have a significant impact on mean performance on basic cognitive tasks and a lesser effect on individual differences.