It is well known that early weaning causes marked changes in intestinal structure and function, and transforming growth factor-beta (TGF-beta) is believed to play an important regulatory role in post-weaning adaptation of the small intestine. The present study examined the distribution and expression intensity of TGF-beta in the small intestinal mucosa of pre- and post-weaning pigs using a specific immunostaining technique and Western blot analysis. The level of TGF-beta in the intestinal mucosa, as estimated by Western blot analysis, did not change significantly during weaning. However, when examined by the immunostaining technique, TGF-beta1 (one of the TGF-beta isoforms dominantly expressed in the tissue) at the intestinal villus epithelium, particularly at the apical membrane of the epithelium, decreased significantly 4 d after weaning, while the staining intensity increased significantly at the intestinal crypts compared with that in pre-weaning pigs. These changes were transient, with the immunostaining intensity for TGF-beta1 at the intestinal villi and the crypts returning to the pre-weaning level by 8 d post-weaning. The transient decrease in TGF-beta1 level at the intestinal villus epithelium was associated with obvious intestinal villus atrophy and marked reduction of mucosal digestive enzyme activities. Furthermore, the number of leucocytes staining positively for TGF-beta1 increased significantly in the pig intestinal lamina propria 4 d after weaning. These findings strongly suggest that TGF-beta plays an important role in the post-weaning adaptation process in the intestine of the pig.