RNA from PC 12 cells was translated in a cell-free system and the peptides synthesized in vitro were analyzed by immunoprecipitation with an anti-T.H. serum raised in Rabbit. Analysis of the immunoprecipitate on a SDS-polyacrylamide gel reveals a major band with a molecular weight of 62000 dalton. A protein of the same molecular weight was also precipitated from a PC12 cell lysate. This molecular weight of 62000 dalton corresponds to the reported for tyrosine hydroxylase purified from PC12 cells.