Streptavidin-metallothionein chimeric proteins with biological recognition specificity in which the streptavidin moiety provides high affinity biotin binding and the metallothionein moiety provides a high affinity metal binding. The binding affinity of the streptavidin-metallothionein chimeric protein both for biotin and heavy metal ions allows specific incorporation into, conjugation with, or labelling of any biological material containing biotin with various heavy metal ions.