Quantitative microchemical study of the tissues comprising fracture callus has been undertaken to correlate the biochemical activity of the bone repair process with its previously established morphological features. Areas of proliferating fibrous tissue, hypertrophic cartilage, new bone and undifferentiated granulation tissue were analyzed for their content of carbohydrate metabolizing and phosphatase enzymes. Fracture callus cartilage is biochemically similar to epiphyseal cartilage. Carbohydrate metabolism provides structural intermediates and energy for bone repair. Inorganic pyrophosphatase removes the inorganic pyrophosphate which accumulates from structural synthesis and prevents its inhibition of new bone calcification. The individual parts of the callus have identical biochemical function regardless of the age or healing time of the fracture callus.