We examined the contributions of dietary protein and mineral to fracture-healing by assessing the mechanical properties of fracture callus in rats that were fed a diet that was deficient in or enriched by these nutrients. In order to isolate the effects of diet on fracture-healing, we developed a method for producing a standard closed femoral fracture with minimum-soft-tissue injury. Three groups of animals were studied. Group I was a control group, in which the rats did not undergo an operation. The rats in Group II underwent intramedullary pinning of the right femur, but no fracture was created. The rats in Group III underwent pinning identical to that used for Group II, after which a closed, transverse femoral fracture was produced. Immediately after surgery, the animals in each group were subdivided into five diet-treatment subgroups. Subgroup A received a regular diet; Subgroup B received a protein-free diet; and Subgroup C received a mineral-free diet that was lacking in calcium, phosphorus, and vitamin D. Subgroup D received a protein-supplemented diet that was composed of three times the calculated requirement of protein, and Subgroup E received a mineral-supplemented diet that was composed of three times the calculated requirements of calcium and phosphorus as well as a therapeutic dose of vitamin D, equivalent to that used in the treatment of osteomalacia. At the end of five weeks, the animals were killed and the right femur of each one was subjected to torsion-testing to failure.(ABSTRACT TRUNCATED AT 250 WORDS)