Abstract: Zeolites having a SiO.sub.2 to Al.sub.2 O.sub.3 ratio of more than 10, particularly ZSM-5 zeolites, are produced by:(a) forming a reaction mixture comprising a silica source, an aluminium source an inorganic base and templating agent and adjusting the pH to 10.7-11.7;(b) heating the reaction mixture whereby zeolite crystals are formed;(c) separating the crystallized zeolite from the reaction mixture leaving behind a residual mixture and calcinating the zeolite to decompose the organic component;(d) adding to the residual mixture templating agent at an amount so as to form a reaction mixture wherein the level of the templating agent is as in the reaction mixture of step (a); and(c) repeating steps (a)-(d), with the reaction mixture obtained in step (d) serving as the source for the templating agent of step (a) and every one or more cycles, treating the residual mixture of step (c) to remove salts therefrom.