Parameter passing is the mechanism by which various program modules share information in a complex program; this paper was a study of novice programmers' understanding of the parameter construct. The bulk of the data was collected from interviews with eight college students enrolled in a state university introductory computer programming course. Observations of the programming instruction, interviews with the course's instructor, and related student work provided additional data. Results revealed that the natural-language meaning of some computer terminology caused problems and most students' understanding of the parameter construct was fragile at the conclusion of their introductory course. Furthermore, it found that students' procedural knowledge (ability to construct modular programs that incorporate parameters) generally surpassed their conceptual knowledge (understanding of the parameter construct and of programs that incorporate the construct). The study also indicated that students who harbored fundamental misconceptions of the parameter process could, by making seemingly innocuous adjustments to procedure heading lines, construct programs that produced the correct answer. Concrete representations, collaboration in a structured laboratory environment, focused completion-type exercises, and elaboration appeared to foster success. Twenty-two appendices provide consent forms, a background survey form, excerpts from the literature, laboratory worksheets, assignments, interview protocols, and programming tasks. (Contains 53 references.) (Author/AEF)