The rate of intestinal absorption was observed in the study in order to evaluate equivalence of two batches of oral suspension dosage forms containing an active ingredient widely used in certain hepatic disorders treatment. The following experimental methods were applied: a) rat mesenterial system perfusion in situ and b) intraduodenal administration in rat. Rats were anesthetized with urethane (1.5 g/kg, i.p.) during the whole experiment. Mesenterial system was single-pass perfused with an influx cannula entering arteria mesenterica superior and with an efflux cannula coming out of vena portae. The system was supplied with Krebs-Henseleit solution (pH 7.4) under a constant pressure of 15 kPa saturated with 95% O2-5% CO2. 6 ml of suspension was given into the intestinal lumen. The small intestine was tied under the bile duct entry and in the place of ileum–caecum junction. In another experimental in vivo set up was the suspension administered intraduodenally in rats with tied small intestine in the same way as in the previous experiment. Blood samples were taken from aorta abdominalis at 1h, 2h, 3h and 4h after suspension administration. Perfusion samples were collected during the following 90 min. Concentrations of absorbed portion were measured. The results were compared each together and used for dosage form equivalence evaluation as well as for optimalization of equable absorption in the terms of pharmaceutical dosage forms changes.