Abstract: A method and apparatus for determining the presence or absence of a disease condition at a test site on a human or animal subject by detecting during a test period the respective electrical potentials of the electromagnetic field present in the subject between each of a plurality of measurement locations in the area of the test site and at least one reference location. A representative potential is separately obtained for each measurement location during the test period, and these representative potentials are compared at the end of the test period to obtain relationships therebetween which are indicative of either the presence or absence of a disease condition.