The ARCS Model of Motivational Design has been used myriad times to design motivational instructions that focus on attention, relevance, confidence and satisfaction in order to motivate students. The Instructional Materials Motivation Survey (IMMS) is a 36-item situational measure of people's reactions to instructional materials in the light of the ARCS model. Although the IMMS has been used often, both as a pretest and a posttest tool serving as either a motivational needs assessment prior to instruction or a measure of people's reactions to instructional materials afterward, the IMMS so far has not been validated extensively, taking statistical and theoretical aspects of the survey into account. This paper describes such an extensive validation study, for which the IMMS was used in a self-directed instructional setting aimed at working with technology (a cellular telephone). Results of structural equation modeling show that the IMMS can be reduced to 12 items. This Reduced Instructional Materials Motivation Survey IMMS (RIMMS) is preferred over the original IMMS. The parsimonious RIMMS measures the four constructs attention, relevance, confidence and satisfaction of the ARCS model well, and reflects its conditional nature.