1. A monolayer cell culture was established from a hypernephroma removed from a patient with the diagnosis of ectopic parathyroid hormone (PTH) production.
2. Culture media contained immunoreactive peptides of a similar size to PTH and several of smaller size.
3. [14C]Leucine and 75Se-labelled methionine added to the media were incorporated into those peptides in the cells and medium which behaved as PTH immunologically and physicochemically.
4. A basic peptide resembling proPTH (the biosynthetic precursor of PTH) was synthesized.
5. Labelled immunoreactive fragments of PTH were found in cells after incubation with radioactive amino acids.