Surface plasmon phenomena are a topic of considerable current interest. We describe a simple experiment and theory for a senior level undergraduate investigation of surface plasmons in silver films. An ∠500‐Å‐thick silver film is evaporated on the hypotenuse face of a right glass prism. Light (p‐polarized) from a He–Ne laser is incident through the prism on the metal film. At an angle of incidence a few degrees greater than the critical angle for total reflection, a sharp minimum in the reflected light is observed, corresponding to the excitation of the surface plasmon. The minimum in the reflectivity results from the absorption of the resonantly enhanced surface plasmon mode in the silver film. The dispersion relation for the surface plasmon and the reflectivity due to the excitation of this normal mode are calculated. Only a modest vacuum of ∠10−3Torr is necessary to produce the required thin silver films.