Few laboratory procedures describe the use of circular dichroism (CD) at the undergraduate level. To increase the number of laboratory exercises using CD, a thermal denaturation study of myoglobin using CD is described to assess protein stability. Values obtained from a more classic linear data analysis approach are consistent with data analyzed with a modern software program that "fits" the data set to a model using a non-linear approach. Both methods gave quantities consistent with reported literature values. (Contains 1 table and 5 figures.)