High resolution spectroscopic study of Abell 78

High resolution spectroscopic data of the central knots and the outer shell of the planetary nebula Abell 78 are analyzed. Chemical abundances and kin ematics were derived for each region. The inner knots appear to be denser a nd slightly cooler than the outer shell, and they are constituted by an ext remely H-deficient material. These knots are receding from the central star with velocities in the range from +40 to -60 km s(-1) and present cometary structures probably caused by the stellar wind. The outer shell appears to have very low metallicity but we conclude that abundance determinations ar e probably affected by large temperature fluctuations in the gas, caused by additional heating mechanisms such as shocks by high speed ejecta and phot o-electrons from dust grains, etc. Our kinematical analysis clearly demonst rates that H lines are not emitted in the inner knots but in the outer shel l. In the outer zone we have detected a high-velocity compact structure, wi th velocities from -40 to 90 km s(-1). This spike emits in collisionally ex cited lines (mainly [O III]), but it is not detected in H or He lines. Ther efore, it should consist of a "bullet" of R-deficient material that is coll iding with the outer shell.