A detailed analysis of more than 800 electronic high-resolution spectra of gamma Cas, which were obtained during a time interval of over 6000 days (16.84yr) at several observatories, documents the smooth variations in the density and/or extend of its circumstellar envelope. We found a clear anticorrelation between the peak intensity and FWHM of the H{alpha} emission, which seems to agree with recent models of such emission lines.