Electromagnetic surveys were carried out in 1982 and 1983 at Qal'at al-Bahrain to locate a large harbor and/or canal system, human burials, and wall structures. An EM-31 noncontacting terrain conductivity meter was applied in two recording modes: 1) vertical dipoles with a depth penetration of approximately 6 meters, and 2) horizontal dipoles with a penetration of approximately 2.5 meters. Two plots of 43 by 75 meters and 46 by 73 meters were measured using a 2-meter interval grid. Conductivity data at each grid point were used to produce contour maps showing the conductivity variations in both modes. Additionally, 15 traverses of one, two, or three parallel lines were measured at either 1 or 2-meter intervals (2771 data points). Based on the field analysis, it was possible to identify areas where the harbor/canal system was present. Furthermore, it was possible to correlate the variation in the conductivity patterns with architectural variation obtained from top-plan drawings. Our data suggests a clear and significant relationship between the manmade features and the variation in conductivity. Final data analysis was made on both 2-and 3-dimensional graphs obtained from the conductivity data.