Two recombinant DNA plasmids were constructed with identical transcriptional and translational regulatory elements controlling expression of the bovine growth hormone (bGH) gene or the bGH gene lacking introns. Transient expression of these plasmids in cultured eukaryotic cells, monitored by assaying secretion of bGH into the culture medium, was employed to examine the relative importance of introns in the expression of this gene. The bGH gene lacking introns is expressed more efficiently than the bGH gene in avian and mammalian cells.