Preprolactin transcripts, synthesized in vitro, were actively translated for a prolonged period when injected into Xenopus oocytes. As a result, prolactin continued to be secreted into the media for up to 6 days after injection of the transcript. To investigate the role of the preprolactin 3' untranslated sequence in stabilizing transcripts, it was fused to coding regions derived from signal recognition particle receptor alpha-subunit or preproinsulin receptor. The translational half-life of the chimeric RNA was increased for both coding regions, suggesting that a sequence within the preprolactin 3' untranslated region that prolongs translation is transferable. Deletion mutagenesis of this untranslated region demonstrated that a sequence of 98 nucleotides immediately following the prolactin stop codon was sufficient to prolong translation of RNAs injected into Xenopus oocytes.