The influence of student personality on the effects of the Personalized System of Instruction (PSI) was examined. Three testing systems (midterm and final exams; bimonthly tests; and PSI) were examined along with three personality dimensions (internal-external locus of control, need for achievement, and need for autonomy). There were no significant differences among test system grades; however, there were significant differences in the students' evaluation of the test systems. The PSI system was seen more favorably on all evaluative and dynamic items, and was seen as stronger. The interaction between test section and personality yielded no significant differences on grades and one significant effect on students' evaluation of how informative the test system was. Students recognized the advantages and the value of the PSI regardless of their personality styles. (Author/PJC)