Molybdenum is one of the major trace elements for plants, but its excess and the deficiency of copper in soils can lead to the production of feed that may be toxic to animals and cause molybdenosis. Menilite shales that occur in the Eastern Beskids Mts. are characterised by an elevated content of this element. The concentration of molybdenum and copper has been determined in samples of bedrock, soils and plants (Trifolium hybridum L. and Plantago major L. plants), taken in the area of occurrence of menilite shales and the Otryt Sandstones. The molybdenum concentration in rocks varies from 0.80 to 40 mg/kg, in soils - from 1.97 to 19.58 mg/kg, and in plant material - from 0.54 to 11.76 mg/kg. The copper concentration in rocks ranges from 11 to 111 mg/kg, in soils - from 23 to 76 mg/kg, and in plants - up to 20 mg/kg. The average Mo concentration in all kinds of plants is significantly higher in the area of occurrence of menilite shales than in the area where the Otryt Sandstones are dominant. The higher content of Mo in the samples collected from clover was accompanied by the lower Cu/Mo ratio, which may cause a molybdenosis disease in animals in the study area.