The relationship between immunohistochemically demonstrable hepatic metallothionein (MT) and age was studied in histologically normal livers from 12 fetuses (13-28 weeks' gestation) and 19 children (birth-4 years). In addition, the relationships between copper (rubeanic acid-positive), copper-associated protein (orcein-positive), lipofuscin (periodic acid Schiff after diastase digestion and Schmorls-positive), and MT (immunostaining) were studied. The fetal livers showed periportal and patchy mid-zone copper-associated protein and lipofuscin granules, together with strong diffuse cytoplasmic and nuclear MT immunostaining. On the other hand, the livers of the children over 6 months of age showed no copper-associated protein or lipofuscin granules, and minimal or no cytoplasmic MT immunostaining (one case showed nuclear MT immunostaining). The DPAS and Schmorls-positive lipofuscin granules appeared to be identical to the orcein-positive copper-associated protein granules which were consistently negative on MT immunostaining. The demonstration of cytoplasmic granular orcein positivity or diffuse non-granular MT immunostaining in liver above the age of 6 months would appear to be of pathological significance.