Eighty patients who had sustained a fracture of the tibial shaft were studied by scintigraphy using technetium-99m labelled methylene diphosphonate (99Tcm MDP) and a gamma camera. Static scintigrams were obtained in the early stages following injury and examined for the presence of 'cold spots' which may indicate loss of blood supply to fracture fragments; these were found in 10 per cent of cases but did not bear any definite relationship to the normal progression of union. Sequential dynamic scintigrams were obtained at intervals up to 20 weeks after fracture to determine whether a pattern of uptake of tracer could be identified which correlated with the subsequent progression of union, but no significant difference was observed between fractures healing promptly (less than 20 weeks) and those in which healing was delayed (greater than 20 weeks).