Objective. To estimate the diagnostic accuracy and the scope of utilisation of a new bio-electronic method of organ diagnostics. Design. Double-blind comparative study of the diagnostic results obtained using organ electrodermal diagnostics (OED), with clinical diagnosis as the criterion standard. Setting. Department of Surgery, Helen Joseph Hospital, Johannesburg. Patients. Two hundred pre-selected inpatients of mean age 38 years (standard deviation 9 years) with suspected pathology of one (or more) of the following organs: oesophagus, stomach, gallbladder, pancreas, colon, kidneys, urinary bladder and prostate. In total, 714 of the abovementioned internal organs were selected for statistical consideration. Main outcome measures. The degree of rectification of the measuring current once the resistance ‘breakthrough effect' has been induced in the skin, as well as the difference in impedance measured at organ projection areas (OPAs) (skin zones corresponding to particular internal organs). Results. In total, 630 true OED results were obtained from the 714 subjects considered, with a detection rate of 88.2% (95% confidence interval (CI): 85.6 - 90.5%). Established OED sensitivity was 89.5% (CI: 85.2 - 92.8%) and OED specificity equalled 87.5% (CI: 84.0 - 90.4%). The predictive value for positive OED results was 81.7% (CI: 76.9 - 85.9%) and for negative OED results 93.0% (CI 90.1 - 95.2%). Healthy organs usually produced the OED result ‘healthy' or ‘within normal limits', while subacute pathology displayed ‘subcute' and acute pathology ‘acute'. The OED results were not affected by either the type or the aetiology of disease, i.e. OED estimated the actual extent of pathological process activity within particular organs but did not directly explain the cause of pathology. Conclusions. So-called OPAs do exist on the skin surface. Pathology of a particular organ causes a related OPA to rectify electrical currents once the resistance ‘breakthrough effect' has been induced in the skin. Pathology of an internal organ also increases the impedance of the corresponding OPA. The degree of rectification or difference in impedance is proportional to the extent of the pathological process within this organ. OED which utilises the abovementioned electrical phenomena of the skin, is a reliable bio-electronic method of non-invasive medical diagnostics, with high rates of sensitivity, specificity and predictive values. OED may be used to detect diseased organs and estimate the extent of pathological process activity. S Afr Med J 2004; 94: 547-551.