A student activity that focuses on the isolation of glucoraphanin from broccoli using preparative high-performance liquid chromatography (HPLC) is presented here. Glucoraphanin is a glucosinolate, whose byproducts are known to possess anticancer properties. It is present naturally at high levels in broccoli and other "Brassica" vegetables. This activity has students practicing and developing a number of skills including liquid extraction; cleanup by solid-phase extraction; analytical HPLC with diode array detection to identify the peak of interest; and preparative HPLC coupled with a fraction collector to isolate the glucoraphanin fraction. It also represents an authentic application of preparative HPLC as glucoraphanin is not readily available from the main chemical suppliers. (Contains 4 figures.)