A process is described for producing synthetic zeolites with a MFI structure, a Si/Al atomic ratio from roughly 8 to 45 and very small primary crystallites, a Si source, an Al source and an organic template being reacted with one another under hydrothermal conditions, the Si/Al atomic ratio being roughly 9 to 50 and the ratio between the longest and shortest axis of the primary crystallites being roughly 1.0 to 1.5:1; the process is characterized in that the reaction is carried out in the presence of seed crystals with an average particle size from roughly 10 to 100 nm, preferably from 20 to 50 nm from an earlier batch without separation from the mother liquor. The zeolites as claimed in the invention which are characterized by the combination of the following features:

• (a) Si/Al atomic ratio 8 to 45:1
• (b) Size of the primary crystallites roughly 0.01 to 0.05 microns;
• (c) Ratio between longest and shortest axis of the primary crystallites: roughly 1.0 to 1.5:1;
• (d) Ratio between the intensity of the x-ray diffraction line with the highest intensity (D_max=3.865+/-0.015) and the intensity of the x-ray diffraction lines of ZSM 11-zeolite (D_max=11.15 angstroms); mordenite (D_max=9.06 angstroms); -cristobalite (D_max=3.345 angstroms); and analcim (D_max=4.83 angstroms)500:1.

One development of the process as claimed in the invention is characterized in that the reaction product is converted by ion exchange into the H form, moldings produced with the addition of binders and optionally catalytically active base metal and/or precious metal components are added before or after the moldings are produced. The synthetic zeolites can be used as catalysts, especially as catalysts for acid-catalyzed reactions, oxidation, reduction and adsorption.