Rats can be used as a model organism to teach physiological concepts in a laboratory setting. This article describes a two-part laboratory that introduces students to hypothesis testing, experimental design, the appropriate use of controls and surgical techniques. Students perform both a castration and sham-control surgery on male rats and test the effects of reduced testosterone due to castration on the weight and histology of seminal vesicles. After performing the surgeries and collecting the data, students learn histological techniques, as well as empirical data collection, analysis and interpretation. Demonstrating the effects of testosterone through castration surgery bridges concepts learned in a traditional physiology class setting with data gleaned from research in a laboratory. Overall, the male castration surgery provides students with hands-on skills and an understanding of the work done by scientific researchers and health care professionals.