The rectal absorption of aminopyrine (AP) from a three-component-system suppository base (TCS), which is a mixture of oleaginous base, water-soluble base and the poly-(oxyethylene) poly-(oxypropylene) block copolymer, Unilube, was investigated. Albino rabbits were used as the animal model. The bioavailability of oleaginous base and water-soluble base (polyethylene glycol 4000) were 44.3% and 82.6%, respectively. The time to reach maximum plasma concentration (Tmax) of the oleaginous and the water-soluble bases were 21.0 +/- 8.2 min and 33.0 +/- 16.4 min, respectively. When TCS was used, its Tmax was 30 min and increasing the amount of Unilube in the base from 5% (w/w) to 20% (w/w) decreased the bioavailability from 100.4% to 47.2%. The softening temperature of TCS was 55-57 degrees C. Collectively, TCS containing 5% of Unilube gave significantly higher bioavailability than the other bases without softening until 57 degrees C. Also, the results of the two different release tests were compared with the results of an animal experiment in this paper.