A novel experimental pH- and time-dependent colonic drug delivery system was prepared and its in vitro and in vivo performances were evaluated. The colonic delivery system consists of minitablets with a big swelling capacity coated with an inlet retardant layer insoluble at all pH ranges but permeable (Eudragit RS 30D) and an outlet layer, insoluble and impermeable at acidic pH but easily soluble at a pH value higher than 5.5 (Eudragit L 55 30D). In vitro results showed that this pharmaceutical system is able to prevent drug release in acidic medium for 2 h but to release its drug content in neutral medium (phosphate buffer, pH 6.8), after 3 h lag-time. In vivo data obtained on 8 healthy volunteers show that the absorption of drug begins after a lag time (tlag) of 2.5 - 3 hours and the maximum plasma level (tmax) was realised after 5.7 hours, suggesting that the release of drug occurs in the colon.