The synthesis of metallothionein (MT) was investigated in three different human epithelial cell lines, each derived from one of the embryonic germ layers. The accretion of different isoforms of the protein was monitored using a sensitive neutral-pH h.p.l.c. method. Induction of MT synthesis by zinc ions and dexamethasone revealed differences between the three cell lines, both with respect to the number and the amounts of the different isoMTs formed. Dose-response experiments showed that an increase in dexamethasone concentration enhances MT accretion asymptotically to a limit, whereas within the concentration range explored zinc produces an exponential augmentation.