Occurrence of pathological changes in wood of various tree species was investigated with an electrical resistance device called Shigometer. Moisture content of wood and content of potassium ions were measured by X-ray fluorescence spectroscopy. Mechanically wounded trees from Ljubljana region and forests near Škofja loka were researched too. Transition between moist sapwood and dehydrated core, as well as biological infection, was well detected by Shigometer in Norway spruce. Electrical resistance measurements were relatively low in infected wood, whereas potassium content was higher than in healthy wood. Lower values of electrical resistance were typical for moist sapwood, and higher values for dehydrated wood. Higher potassium concentration was related to higher electrical resistance readings. Sapwood, discolored wood, decayed wood, wet and dry spots, as well as position of reaction zones, can be detected by Shigometer in diffuse porous woods. Border between sapwood and heartwood in diffuse ring-porous wood can also be detected by Shigometer measurements. Electrical resistance of heartwood was higher than in healthy tissues of black locust, oak and European chestnut. Infected tissue had lower values of electrical resistance. Potassium content was higher in sapwood than in heartwood.