The behaviour of a single 1-g oral dose of azodisal sodium (ADS) given to 10 healthy volunteers with an ileostomy was studied. Blood samples were drawn at various times, and urine and ileostomy fluid were collected during the following 24 h. ADS was absorbed to a very low extent, giving a maximum serum concentration of less than or equal to 5.1 micrograms/ml within 0.5-2 h after the dose was ingested. A mean of 0.3% of the dose was excreted in unchanged form with the urine. The metabolites 5-ASA and Ac-5-ASA could not be found in serum or urine. Of the ADS dose given, 100.2% (SD +/- 14.8%) could be recovered in the ileostomy fluid. The results indicate that ADS is a potentially useful drug for the local treatment of ulcerative colitis, 5-ASA being the active part of the molecule.