Simultaneous membrane based solvent extraction (MBSE) and membrane based solvent stripping (MBSS) of 5-methyl-2-pyrazine carboxylic acid (MTCA) in hollow fibre contactors with solvent containing trioctylamine (TOA) have been studied. An effective transport of MPCA was achieved. The analysis of mass-transfer resistances showed, that the kinetics of the acid-carrier complexes formation and/or decomposition should be taken into account. The contribution of the mass-transfer resistances based on reaction kinetics to the overall resistances in MBSE and/or MBSS is from 40 to 80%. The proposed reaction-diffusion model gives a much better fit to the experimental values than a pure diffusion model. The mean value of the lumped rate constant of the extraction reaction for MPCA is 14.2(<^>) x 10(4) m.s(-1). Depending on the stripping solution composition, i.e. aqueous solution of NaOH or aqueous solution of NaOH with an addition of NH4OH with lower basicity, the mean value of the lumped rate constant of the stripping reaction is 6.02 x 10(-6) m.s(-1) and 2.65 x 10(-6) m.s(-1), respectively. It has been found that sulphuric acid is co-transported with MPCA. An excess of H2SO4 in the feed decreases the selectivity of NTCA separation. The molar ratio of the transported H2SO4 to MPCA decreases with increasing the MPCA concentration in the solvent. When the feed solution pH was kept at 2.2 the value of this ratio ranged from 1 to 2.5, while when it was kept at 2.5 and NH4OH was added to the stripping solution, the molar ratio of the transported H2SO4 to MPCA was in the interval from 0.2 to 1.5.