With molecular biology permeating nearly all areas of biology, the study of gene regulation has become a central part of even introductory courses in college biology. All too often, however, we find students memorizing the facts of the material they're being presented, without much understanding of the concepts behind how genes are actually regulated. In 1993, Rodney Anderson published an excellent lab for studying gene expression in this journal (Anderson 1993). His 50-minute lab investigating the bacterial lac operon works well, and is not unlike the somewhat longer one I had been using for many years in my freshman genetics class. However, my students have found my lab conceptually difficult, and responses on exams showed that they came away with little understanding of gene regulation or of the experiment itself. On the semester-end evaluations, many students suggested I eliminate this lab from the course. Last year, I converted the lac lab to a discovery lab. This lab requires significantly more time, preparation and discussion than that published by Anderson, but it has been well worth it. I have found students come away from this lab understanding the regulation of the lac operon, and enjoying the experience as well. The major differences in the procedures are the addition of more controls, including the analysis of a lac z strain that cannot synthesize the ,B-galactosidase enzyme, and having the students themselves prepare the bacterial samples with various strains and sugars, rather than