The activity of femoral vessels in delayed bone scans was evaluated visually in 237 consecutive patients and quantified in 40 female patients. In visual analysis the patients were randomly divided into three groups and in quantitative analysis into four groups of equal size. Two different MDP preparations and one DPD preparation were used as bone-seeking agents. With aging, the activity in femoral vessels increased with all agents in visual analysis, significantly with MDPs (P<0.001) between="" patients="">60 years and >60 years. In female patients with all agents a significant increase in femoral activity was found (P<0.001 with="" mdps,="">P<0.05 with="" dpd).="" in="" patients="" 60="" years,="" the="" femoral="" uptake="" was="" significantly="" higher="" with="" mdp="" when="" compared="" with="" the="" dpd="" uptake="">P<0.01 with="" mdp1,="">P<0.05 with="" mdp2).="" between="" the="" mdps="" no="" significant="" differences="" were="" found.="" in="" quantitative="" analysis="" the="" femoral="" vessel="" to="" soft="" tissue="" ratio="" was="" significantly="" higher="" in="" patients="">70 years when compared with patients 50 years with MDP. No difference was found with DPD. Histological examination of excised arteries of ten patients with intense femoral uptake of MDP showed arteriosclerosis and calcification in all cases. The findings suggest that the femoral visualization in delayed bone scans is probably related to arteriosclerosis and is not a non specific finding. There may be age-related differences in the distribution of MDP and DPD.