In seven patients suffering redisplacement, nonunion or segmental collapse after nailing of femoral neck fractures, subsequent changes in the vitality of the femoral head were studied with tetracycline labeling and 99mTc-MDP scintimetry. At reoperation (total hip arthroplasty), the femoral heads were extracted and sawn into slices which were then analyzed. Vitality before nailing was totally lacking (tetracycline labeling) in one case (nonunion), and in the remaining cases moderate reduction was seen, most pronounced in the apical part of the head. In all cases, scintimetry 1-2 weeks after nailing showed reduced femoral head uptake of 99mTc-MDP, but scintimetry some hours before reoperation showed increased femoral head uptake. Isotope analysis of the slices from the extracted femoral heads showed marked reduction of uptake in the apical part of the head, moderate reduction in the distal and anterior parts, and satisfactory uptake in the posterior part of the head and the foveal region, though with individual variations. It was concluded that there is a genuine increase in uptake (revascularization) later in the course in postoperatively avascular heads, and that the apical part of the femoral head sustains the most pronounced vascular damage in femoral neck fracture and is probably the slowest to revascularize.