The psychological characteristics of programmers are believed to be important determinants of programming productivity. However, little evidence is available to support this contention. This investigation, motivated by the lack of such evidence, was concerned with determining the influence of the programmer's cognitive complexity (differentiation and integration) and experience on comprehending and modifying programs of different levels of complexity. Data were collected from ninty-three graduate and undergraduate students in a classroom experimental setting. In the first phase of the experiment, a background questionnaire was administered in order to collect experience and other demographic information. Also, a domain-specific Role Construct Repertory (REP) Test was administered to collect cognitive complexity information. In the second phase, the subjects were randomly assigned to either the program comprehension group or to the program modification group. Both groups used two COBOL programs of differing levels of complexity to do comprehension and modification exercises. Three sets of hypotheses were tested. The first set of hypotheses was designed to evaluate the direction and strength of the relationship between cognitive complexity and program comprehension and modification. The second set of hypotheses was designed to evaluate the combined influence of cognitive complexity and program complexity on the comprehension and modification of …