The specific regulation of pancreatic elastase I and II mRNA expression as well as of the protein, RNA, and DNA contents were determined during ontogeny in the calf. Specific activities and mRNA concentrations were quantified by spectrophotometry and reverse transcriptase-polymerase chain reaction, respectively. Calves were either milk-fed or weaned until slaughter at different ages. The biosynthesis of elastases I and II was modulated by postnatal development and weaning, leading to specific gene expression profiles. The levels of elastase I activity and of the corresponding mRNAs were found to evolve in a roughly similar way. On the contrary, elastase II activity level decreased sharply during postnatal development, while no changes were observed in the corresponding mRNA levels. After weaning, elastase I activity and mRNA levels, as well as elastase II mRNA levels, increased. However, the magnitudes of elastase I activity and mRNA inductions were different. Therefore, the expression of each gene in the calf pancreas is more or less independently regulated and the regulation is mainly pretranslational (elastase I) or translational (elastase II) during postnatal development and both pretranslational and translational at weaning. The translational efficiency of elastase I and II mRNAs might be influenced by the nature of dietary proteins.