The composition of the solid and liquid phases in the course of synthesis of zeolite ZSM-5 by the "fluoride method" has been monitored using C-13, Al-27 and Si-29 MAS NMR (solid), by C-13, F-19 and Si-29 NMR (liquid) and by atomic absorption spectrophotometry. The degree of crystallinity of the solid phase was assessed by X-ray diffraction. The silicon content of the mother liquor never exceeds 5% of the total silicon content, and the aluminium content is always below 1% of total aluminium. We discuss the successive steps in the synthesis.