Aminopeptidase activities were studied biochemically from the supernatants of the homogenates prepared from the normal and post extraction palatal mucosa of the rat. The determinations were carried out at 0.5, 1, 2, 4, 8 and 16 hours and 1, 2, 3, 5 and 7 days following extraction using N-L-aminoacyl-2-naphthylamines of arginine, glycine, leucine, proline and valine as the substrates. In addition, in the second part of the study the hydrolysis ofN-L-aminoacyl-2-naphthylamines of alanine, histidine, isoleucine, lysine, phenylalanine, serine, threonine, tyrosine and valine was tested at I, 3 and 5 days following extraction. The effect of chloride ions (0.2 M NaCl) on the hydrolysis of arginine and lysine derivatives was also tested. The specific activities of aminopeptidases obtained from the extraction-wound side were compared to those of the control side at each time interval. Tooth extraction caused a considerable reduction in the specific activities of aminopeptidases in the surrounding palatal mucosa immediately after extraction (at 0.5 hr.). The specific activities in the wound tissue remained generally below the control levels for 24 hours and reached their maximum within 5 days following extractions. The highest relative increase was obtained with N-L-valyl-2-naphthylamine. Arginine aminopeptidase was activated by chloride ions on an average 20 per cent more in the wound tissue than the control. This effect can be considered suggestive of the activation of aminopeptidase B in the post extraction palatal mucosa.