A novel radiochemical method for investigating the catalytic transformations of the C-11-radioisotope labeled methanol over H-ZSM-5 and H-Beta zeolite catalysts has been introduced. The catalysis process was monitored by gamma detectors and the C-11-labeled products were analyzed by radio-gas chromatography. The medium pore H-ZSM-5 and H-Beta zeolite catalysts were synthesized and characterized using X-ray powder diffraction, scanning electron microscope, nitrogen adsorption, X-ray fluorescency and FTIR spectroscopy. The investigations of C-11-labeled product distributions and reaction mechanism of the conversion of [C-11] methanol over H-ZSM-5 and H-Beta zeolite catalysts have been elaborated in terms of structure and acidity of the catalysts. In microreactors the effect of natural carbon compounds from environment can be a disturbing effect for the detection of inactive carbon products. Applied radio detection method eliminates these disturbing effects and detects only C-11-labeled compounds during the whole catalytic process. In the study of the transformations of carbon compounds, besides the well known C-14 tracer technique and C-13 MAS NMR spectroscopy investigation, the C-11-method is a new, more sensitive and simple one to monitor the transformation of the starting C-11-labeled compound by radio detectors ( gamma detector) and for analyzing the C-11-labeled products by radio-gas chromatography.