Pertraction of dimethylcyclopropanecarboxylic acid (I)MCCA) and phenol in a new hollow-fiber (HF) contactor of three liquid phases with distributed U-shaped bundles of microporous HF was studied. Trioctylamine (TOA), Hostarex A327 and Cyanex 47 1 X have been used as carriers. The performance of this contactor is similar to other HF contactors. Its advantage is that both bundles of fibers can elongate without deformation of fibers and maldistribution of fibers in the bundles. Pulsation of the membrane phase increases the transport rate by 35-61% and it reaches a plateau value at the pulsation velocity of about 1.1 mm s(-1). With increasing velocity of the feed in the fiber lumen the value of the overall mass-transfer coefficient increases, but soon a steady value is approached at the velocity of about 5.5 cm s(-1). The diffusion resistances in a series model do not describe the pertraction of DMCCA well. The suggested new diffusion-reaction model, considering the resistance based on the kinetics of the stripping reaction, fits experimental data well. Not only the rate of the acid-carrier complex decomposition, but also that of the DMCCA dimer decomposition have to be considered. The estimated values of the apparent reaction rate constant were for the membrane with TOA 1.91 X 10(-6) m s(-1) and for pure n-alkanes 5.78 x 10(-6) m s(-1). The kinetic resistance on the stripping interface represents 20-60% of the overall mass-transfer resistance and its value is comparable to the diffusion resistance of the both walls.