Adenosine deaminase (ADA; EC 220.127.116.11) is a purine catabolic enzyme causing hydrolytic deamination of adenosine and 2'-deoxyadenosine to inosine and 2'-deoxyinosine. In the present study, the normal endogenous activity level of ADA was investigated in different regions of the gastrointestinal tract (GIT) during postnatal development of chicken. The effects of corticosterone and dibutyryl cAMP (Bt(2)-cAMP) were studied at two selected postnatal ages. The results indicated a significantly high level of ADA at day 1 in all the regions of GIT, which then declined (-34% in esophagus, -35% in crop, and -48% in small intestine) at day 10 and remained fairly constant till day 90. While in the proventiculus, the activity of ADA decreased (-30%) at day 30 and showed further decline (-52%) at day 90 as compared to day 1. Corticosterone was seen to significantly decrease (-23 to 79%) the activity level, depending on the regions of GIT studied except proventriculus. The magnitude of decline was more pronounced at day 60 compared to day 10. Bt(2)-cAMP, on the other hand, caused a significant increase (+21 to 67%) in the activity level of ADA again depending on the regions of GIT studied except crop. Western blot analyses also depicted that the decrease and/or increase, respectively, of ADA activity by corticosterone and Bt(2)-cAMP was at the ADA protein level. In conclusion, the study suggests that the ADA activity level is highest at day 1 in all the regions of chicken GIT and could be reduced or enhanced by corticosterone and dibutyryl cAMP, respectively, in an age-specific manner.