Several archaeological sites containing different artifacts were investigated by magnetic and geoelectric measurements. Kilns of medieval semisubterranean houses, ruins of a Roman brick building, and pits of a Copper Age settlement were discovered by magnetic methods. The ground plan of a Roman fortress was determined by resistivity measurements at a location where excavation was impossible because of the high groundwater level. Resistivity measurements made of a Roman homestead to determine the location of a building are discussed in detail. By correlating characteristic maxima of filtered resistivity data, the placement and orientation of walls could be determined. From the measurements, the position and extension of a group of buildings were defined. Prehistoric mining trenches can be located on the basis of anomalously low resistivities. The exact location of a 50000-year-old flint mine on the outskirts of Budapest by geoelectric measurements was defined. A three-dimensional picture constructed from apparent resistivities associated with different penetration depths agrees fairly well with the shape of the ancient mine trenches excavated later. -- AATA