Summary: Zeolites (eight species) and the associated secondary minerals (minerals akin to zeolites, chlorites and related minerals, silica, and calcite) in the Deccan Traps of Western India have been examined in some detail on the basis of chemical, optical, and X-ray studies. The three zeolite zones (laumontite, scolecite, and heulandite, in ascending order) suggested by Walker have been recognized. Efforts have been made to understand their genesis. On available field and laboratory data it is suggested that the different zones of zeolitization are the result of increasing depth and the action of the circulating fluids on the rocks. The activity of such solutions was probably enhanced in the wake of the structural disturbances and intrusive activity that affected the rocks of this area.