 measurements of lead in bone have recently become the focus of research because a ) bone lead levels serve as a cumulative dosimeter of lead exposure over many years ( because of lead 's long residence time in bone ) , and cumulative exposure may be more predictive of chronic toxicity than recent exposure , which is what blood lead levels mostly reflect ; b ) there is suspicion that heightened bone turnover ( e.g. during pregnancy , lactation , and aging ) may liberate enough stored lead to pose a significant threat of delayed toxicity ; and c ) although lead exposure has largely declined in the united states over the past 10 to 15 years , decades of heavy environmental pollution have resulted in significant accumulation of lead in bone among most members of the general u.s . population . 
 epidemiologic research on the impact of lead stored in bone is now possible with the development of 109cd k - x - ray fluorescence ( kxrf ) instruments for the in vivo measurement of lead in bone . in this paper , 
 the kxrf method will be briefly reviewed , followed by a summary of several superfund - supported studies ( and others ) of blood lead and kxrf - measured bone lead in which these measures are compared as biologic markers of lead dose . 
 measurement of bone lead in epidemiologic studies has proved useful in exposure assessment studies , i.e. , in identifying factors that contribute most to retained body lead burden , and in investigating cumulative lead exposure as a risk factor for poor health outcomes such as hypertension , kidney impairment , cognitive impairment , behavioral disturbances , and adverse reproductive outcomes.imagesfigure 1 
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