A series of natural proteins and partially hydrolyzed proteins (peptones) from various animal and plant sources have been tested for the ability to prevent the formation of barium sulfate and calcium carbonate scaling for use as environmentally friendly scale inhibitors (SIs) in the petroleum industry. All SI performance experiments were carried out in a dynamic tube blocking rig at 100 degrees C and 80 bar. Although many of the proteins/peptones showed poor or negligible performance, the milk proteins, casein peptones, and tryptones showed reasonable inhibition performance on the sulfate scale although not as good as some commercial nonpolymeric aminophosphonate scale inhibitors such as diethylenetriaminepentakis-(methylenephosphonic acid) (DTPMP). On the calcium carbonate scale, Tryptone N1 19553 outperformed DTPMP. In addition, the best proteins/peptones showed excellent calcium compatibility. Thermal aging studies indicated that the best peptones were not stable for squeeze treatments at 100 degrees C and therefore are best used for topside continual injection. Several attempts were made to derivatize the pendant primary amine (from lysine) or hydroxyl groups in the proteins to increase the number of carboxylate groups or introduce phosphonate or sulfonate groups. Although scale inhibition performance enhancement was achieved, this could simply be due to synergistic behavior between an unreacted or hydrolyzed starting material and the protein.