Abstract: Protein and other useful products are recovered from animal bone by comminuting fresh bone to small particles which are defatted and then demineralized by maintenance in suspension in hydrochloric acid in a bone/acid counterflow treatment carried out by passing the bone particles through a series of tanks in counterflow with hydrochloric acid passed through the tanks in the reverse direction. Between the tanks the bone/acid mixture is separated and delivered to the respective successive tank in counterflow. After completion of the acid treatment the demineralized bone is separated and washed to produce the final product.