Aldosterone is the most important mineralocorticoid hormone regulating water and electrolyte absorption in the distal convoluted tubule of the kidney. Recently, we detected the presence of the whole chain of aldosterone production from the precursor corticosterone, transcription factor liver receptor homologue-1 (LRH-1), the aldosterone synthase enzyme protein (CYP11B2) as well as the gene to the final product aldosterone in murine large intestine. Here, we decided to correlate the amount of this synthase protein with its enzymatic activity in different parts of gastrointestinal tract and also with the aldosterone concentration in the respective tissue. Considering the physiological behavior of the animals in light and dark environment, we measured these variables at four time points - two in the light, the others during darkness. In vitro activity of CYP11B2 was measured as the amount of aldosterone formed from the precursor deoxycorticosterone using enzyme preparations from homogenized intestinal sections. CYP11B2 enzyme activity was higher in the large than in the small intestine. In ileum and colon, the CYP11B2 activity increased in the dark time. The highest aldosterone concentration was detected in the dark in the large intestine. In summary, enzyme activity of CYP11B2 was present in all parts of intestine; the large intestine formed more aldosterone during the darkness. No difference was seen in any of the variables between the early and late light hours.