A late, i.e. delayed, effect of lead on kidney function and blood pressure was studied in 23 workers with a history of occupational lead poisoning. Twenty lead exposed workers with no known history of lead poisoning were a positive control. Four important factors out of 11 combined variables derived from 22 single variables were identified by factor analysis. The first factor comprised the variables kidney function, blood pressure, age, duration of lead exposure and the number of previous lead poisonings. The second factor comprised the variables duration of lead exposure and biological indicators of lead exposure. The third factor correlated the frequency of previous lead poisonings with the renal blood flow, erythrocytic protoporphyrin and age. The fourth factor comprised the variables length of work service, creatinine clearance and erythrocytic protoporphyrin. The results confirm the presence of the adverse late effect of previous occupational lead poisoning on kidney function regardless of treatment. The phenomenon is not a single event but a complex interplay of past lead poisoning, duration of exposure to lead, "normal" age effect on an increase in systolic and diastolic blood pressure and blood creatinine and a decrease in renal function as revealed by decreased creatinine clearance and a slow down in renal flow time. The complexity of dealing with the confounding variable of age and lack of appropriate classification of renal function impairment may account for the conflicting results of chronic lead effect upon kidney function in the past. The kidney appears to be a critical target organ, reflecting the total lead body burden in chronic lead exposure and poisoning. Therefore monitoring of kidney function in lead exposed workers needs to be mandatory.