A laboratory exercise is presented that incorporates constructivist principles into a learning experience designed for upper-level university biology courses. The specific objectives for this exercise are as follows: (1) To introduce students to cancer biology and to the regulation of programmed cell death as part of the cell cycle; (2) To engage students in scientific inquiry through experimental design and testing, using a constructivist approach; and (3) To encourage cooperative learning in a scientific laboratory setting. This exercise uses a modified Terminal deoxynucleotidyl Transferase Biotin-dUTP Nick End Labeling (TUNEL) assay to investigate apoptosis in human cheek cells. (Contains 3 figures and 2 tables.)