In eight healthy volunteers accelerated intestinal transit time was induced with bisacodyl, and urinary and faecal excretion of sulphasalazine, olsalazine, 5-aminosalicylic acid (5-ASA), and acetyl-5-ASA was studied after a single oral dose of 3.3 mmol sulphasalazine, olsalazine, Pentasa, and Salofalk and 2.6 mmol of Asacol. The faecal and urinary excretion of acetyl-5-ASA was lowest after intake of sulphasalazine and olsalazine and highest after intake of Pentasa and Salofalk. The figures for Asacol were intermediate. This indicates insufficient release of 5-ASA from sulphasalazine and olsalazine. When the results of this study are compared with those of a previous study without accelerated transit time, the disposition of 5-ASA from all the 5-ASA-delivering drugs is influenced unfavourably by an accelerated gut transit but most pronounced in the case of sulphasalazine, olsalazine, and Asacol. The impaired release from the azo compounds sulphasalazine and olsalazine is a result of far less complete splitting of the diazo bond.