This experiment targets undergraduate students in an analytical or organic instructional context. Using a simple extraction, this protocol allows students to quantify and qualify monoterpenes in essential oils from citrus fruit peels. The procedures involve cooling down the peels by immersing them into icy water. After a few minutes, the chilled peels are pulped in a simple kitchen blender using acidic brine to hydrolyze the undesired fatty acids. Essential oils are extracted from the emulsion using methylene chloride and are then injected in a gas chromatograph coupled with a mass spectrometer. Among the fruit tested--limes, grapefruits, and oranges--all showed a high concentration of ("R")-limonene, a monoterpenoid commonly found in these fruits. Students are invited to quantify ("R")-limonene in the extracts following an accurate 5-point standard calibration curve. For students, this experiment may be a first contact with the analysis of plant extracts as well as an introduction to the biochemistry of monoterpenes. (Contains 2 figures, 2 tables and 1 note.)