OBJECTIVE To describe 6 h urinary lead excretion (6 h PbU) after 1 g intravenous ethylene diamine tetraacetic acid (EDTA) in organolead manufacturing workers with mixed exposure to organic and inorganic lead; to determine the predictors of lead excretion (PbU); and to determine the extent to which internal lead stores and ongoing external exposure govern blood concentrations of lead (PbB). METHODS A case series of 21 active workers were studied. Personal industrial hygiene data, grouped by 29 exposure zones, in combination with personal interviews about work location and times were used to derive several measures of recent and cumulative exposure to organic and inorganic lead. The average exposure intensities assigned to the 29 zones ranged from 4 to 119 micrograms/m3 (0.02-0.57 mumol/m3 as lead) for organic lead and from 1 to 56 micrograms/m3 (0.004-0.27 mumol/m3) for inorganic lead. RESULTS After controlling for age, 6 h PbU was significantly and positively correlated with summary measures of PbB--for example, lifetime peak PbB, time weighted PbB--and zinc protoporphyrin concentrations--for example, lifetime peak zinc protoporphyrin, time weighted zinc protoporphyrin--but not with measures of estimated external exposure--for example, duration of exposure and cumulative exposure to inorganic or organic lead. Among workers with higher chelatable lead burdens (6 h PbU > or = 212.4 micrograms (1.03 mumol) divided at the median), there was no apparent relation between recent inorganic lead exposure and PbB at the time of chelation. Among workers with lower chelatable lead burdens (6 h PbU < 212.4 micrograms (1.03 mumol) however, there was a significant relation between exposure and effect between recent exposure to inorganic lead and PbBs. CONCLUSIONS These findings are consistent with the concept of physiological dampening. The high chelatable lead burden, a source of internal exposure, dampens the effect of external exposure on PbBs. The data suggest that in organolead workers with high chelatable lead burdens, PbBs may be more influenced by internal lead stores than by variations in airborne exposure to organic and inorganic lead.