Reported is a study of the relationship between degree of concept relatedness of an instructional sequence and a person's locus of control orientation. Locus of control orientation for the 541 high school biology students involved in the study was evaluated as measured by the adult Nowicki-Strickland scale. The experimental instructional treatment stressed conceptual relationships through conceptual cues and concept mapping exercises, while the control treatment did not. Dependent variables measured were scores on a meaningful learning posttest and on a six-week retention test. Two-way analyses of covariance by treatment and by locus of control resulted in a significant treatment-locus of control interaction effect for retention test scores. Subjects with an external locus of control orientation who were exposed to the experimental treatment outperformed the control group. However, students with an internal locus of control orientation retained the same amount of information regardless of treatment group. (Author/WB)