Abstract An international co-operative blood-Pb interlaboratory study and a Canadian co-operative blood-Pb interlaboratory study were conducted using freeze-dried bovine blood samples with different endogenous Pb levels. The samples were prepared from whole blood of a nonexposed cow and another fed with a single dose of lead acetate. The mean values computed for the two samples analyzed by 25 international participants from 13 countries were 55 and 250 μg Pbl −1, respectively. These results showed a positive bias of 10% for the low level and 9% for the high Pb level with respect to the reference values obtained by isotope dilution mass spectrometry. In the case of the Canadian interlaboratory survey the mean values computed for the two samples analyzed by the 12 participants were 40 and 229 μg Pbl −1, respectively. These results showed a negative bias of 20 and 0.4% in relation to the target values of 50 and 230 μg Pbl −1, respectively. Despite such a bias, the data, on the whole, were of acceptable precision and accuracy when compared with previous interlaboratory blood-Pb surveys.