In the present investigation an optimized semi-quantitative RT-PCR was applied to detect the PR-39 gene expression difference in femur marrow of piglets at different ages by using 18S rRNA as inner marker. Samples were taken at birth, 3, 14, 23, 28 days of age respectively. The results showed that day age affected PR-39 mRNA levels in femur marrow significantly (P 〈 0.05), the expression of PR-39 mRNA was the lowest at birth, then increased remarkably at 3 days of age, but the expression at 14 d-old was lower than t...