[en] Consecutive short bombardment of thick biological specimens with proton beams demonstrated that the yield from oxygen decreases with increasing amounts of total deposited beam; those from carbon and sulfur appear not to be affected, while significant yield increase are observed with respect to the ß-ray yields of all the other investigated isotopic nuclear reactions. The yield alterations were investigated in freeze-dried plant and animal specimens as well as in targets prepared by air drying at several temperatures. Only in ashed specimens do the ß-ray yields remain constant as a function of increasing amounts of deposited beam. The yield alterations induced by the beam on non-ashed biological specimens depend on (I) the total dissipated beam charge, (II) energy of the beam, (III) chemical element, (IV) origin of the biological specimen, and (V) method of preparation of the target. The underlying mechanism and implications of the yield alterations in the elemental analysis of non-ashed biological specimens are investigated and discussed. (author)