Determination of lead (Pb-B) concentration and δ-aminolevulinic acid dehydratase (ALAD) activity in the blood were carried out as means of the specific health examination of lead in workers exposed to lead in a television bulb manufacturing plant. These 330 workers were divided into four groups according to the levels of lead in the air, mean levels of lead in the air of the four groups being as follows: A group 2.4μg/m3, B group 12.5μg/m3, C group 24.5μg/m3 and D group 44.5μg/m3. Comparisons were made among the four groups as to the relationship between ALAD activity and Pb-B levels, the difference of ALAD activity at the same levels of Pb-B, and the relation between ALAD activity and the duration of exposure to lead. Furthermore, recovery pattern of ALAD activity after the exposure to high levels of lead was examined. The following results were obtained: (1) Group pattern indicated by the scatter diagrams of Pb-B and ALAD activity was very similar in A as well as in B groups, but in the other groups it was different and negative correlation between Pb-B and ALAD activity was obtained only in C group (r=-0.404). (2) When the levels of Pb-B were divided into 5μg/dl intervals in four groups, differences of mean values of ALAD activity corresponding to the same levels of Pb-B were apparent among B, C and D groups. It seemed that ALAD activity was affected by smaller amount of lead than the amount affecting the levels of Pb-B. (3) ALAD activity was lower in workers employed less than one year in four groups and thereafter it recovered in three (A, B and C) groups but the recovery rate was different among these three groups. (4) From the recovery pattern of Pb-B and ALAD activity in volunteers after the exposure to lead, lead levels were estimated for workers temporarily exposed to high levels of lead in the air.
