Geophysical prospecting methods can provide valuable information for archaeological site surveys provided that physical contrast exists between the structures and their surrounding terrain. Under such conditions, electrical, magnetic or electromagnetic methods allow archaeological remains to be located from the surface and their lateral extension can be delineated with no soil disturbance. Reconnaissance of ancient roads of the Roman period or later, visible on some aerial photographs of the Plateau vaudois, is a task well suited to geophysical prospecting. The paper presents a brief description of the resistivity instrumentation designed especially for archaeological prospecting. The Wenner (AB=3 m) and the pole-pole (AM=1 m) arrays were carried out during the survey. The conductivity meter EM-31 was also tested on a profile. The results confirm the presence of the ancient roads described or illustrated in local archaeological literature. At one site, the presence of a road was able to be verified through the inspection of a canalisation trench, Comparisons are made with some other examples of Roman roads detected by comparable resistivity methods. Model tank experiments were also conducted in order to compare the geophysical response with field results, and good agreement was found. The methodology developed in this study seems efficient and well adapted to the detection of ancient roads and should prove a valuable tool in further field investigations.