In vitro dissolution profiles of three controlled-release mesalazine formulations were determined at pH 1.0, 6.0 and 7.5. A closed-column type dissolution apparatus was used. A reproducible gradual dissolution profile was seen for Pentasa at all pH values. Dissolution starts immediately and is complete after 20 h. Dissolution profiles at pH 1 and pH 7.5 are much alike and dissolution is faster than at pH 6. The behaviour of Asacol at different pH values corresponds with the expectations: no release at pH 6 and pH 1, fast release at pH 7.5. Dissolution starts after 1 h and is complete after 3 h. Mesalazine release from Salofalk tablets at pH 7.5 and pH 6.0 starts after 2 and 3 h, respectively, and is complete after 5 and 10 h. However, after a long lag-time (10 h) mesalazine is also released from Salofalk tablets at pH 1 and dissolution is complete after 23 h.