Although previous research has indicated no significant relationship between sequencing of programed instructional materials and terminal achievement, it is felt that certain conditions might produce such a relationship. In order to test this idea, a hierarchy of word meanings was constructed, in which each definition was dependent on the previous one. The hierarchy was divided into several different linear and scrambled versions according to the amount of memory and information reorganization required to learn the material. The linear and scrambled versions were then administered to two groups of 80 high school students. Factoral analysis of results showed a significant difference in achievement between students using the linear version and those using a scrambled version for the lower degrees of memory requirement. However, there was no difference in achievement at the higher levels of memory requirement. Conclusions were that sequence does have an effect in programed instruction when a certain optimal memory load is not exceeded, and that further research should be done on the learning mechanisms involved in programed instruction. (RT)