Serum apolipoproteins (Apo) A-I, A-II, B, C-II, C-III and E were determined in healthy Japanese subjects (male 1,603, female 1,800, aged 4-95 yr) by the turbidimetric immunoassay, with six kinds of automated instruments, and the commercial reagent kits with standards. There was a high degree of interlaboratory comparability of analytical values among the 15 participating laboratories. The reference values were calculated for adult males and females (male 677, female 467, aged 21-60 yr). Apo A-I and E levels were significantly higher and Apo C-II and C-III were significantly lower in females than in males. Furthermore, serum Apo A-I and A-II tended to decrease, and Apo B to increase with age. Apo C-II, C-III and E tended to decrease after 60 yr of age.