Positronium. (Ps) formation and interactions were investigated in zeolites. Positron annihilation (PA) lifetime spectroscopy, Doppler-broadening and the recording of the annihilation radiation energy distribution were applied to faujasite X and Y, silicalite-1 (by composition pure SiO2), ZSM-5 and mordenite. The dependence on heat treatment, sample evacuation and gas filling or water content was investigated. Lifetimes over 130 ns and Ps-fractions of 30-40% were found. Various PA techniques yield data with unexpected features for various samples.