The assumption that the first four cognitive levels of the taxonomy of educational objectives are arranged hierarchically and that this hierarchy is cummulative was evaluated. Mental ability and motivation scores were used to divide 144 high school biology students into six blocks. A 93-frame program in genetics was administered, and at the completion of the program the subjects took a 28-item posttest that had subscores for the cognitive levels of knowledge, comprehension, application, and analysis. Results indicated that no significant differences were found between knowledge and comprehension or application and analysis. A significant difference was found beyond the .0005 level, however, between comprehension and application. These results indicate that the cognitive processes at work at each level of the taxonomy may not be equitable, and that the previously mentioned assumptions are at least questionable.