Analysis results from ASCA and ROSAT observations of the narrow-line Seyfert 1 galaxy Mrk 766 are reported .
In the ASCA observation we observed rapid variability with a doubling time scale of 1000 seconds .
A spectral variability event was observed in which the spectrum softened and hardened above and below \sim 1 keV , respectively , as the flux increased .
The spectra could be modeled with 5 components : a power law , warm absorber , iron K \alpha line and soft excess component flux .
The spectral variability resulted from a highly significant change in the intrinsic photon law index from \Gamma \sim 1.6 to \sim 2.0 , an increase in the warm absorber ionization , and a marginally significant decrease in the soft component normalization .
A \sim 100 eV equivalent width narrow iron K \alpha line was detected in the high state spectrum .
Spectral hardening during flux increases was observed in three ROSAT observations .

The change in intrinsic photon index and disappearance of the soft excess component in the ASCA spectra can be explained as a transition from a first order pair reprocessed spectrum to a pair cascade brought about by a sudden increase in the injected electron Lorentz factor .
The change in the ionization of the warm absorber , though model dependent , could correspond to the increase in flux at the oxygen edges resulting from the spectral index change .
The ROSAT spectral variability can be interpreted by variable intensity hard power law and a relatively nonvarying soft component , possibly primary disk emission .
These results are compared with those reported from other narrow-line Seyfert 1 galaxies .