We have been carrying out a program of monitoring light and velocity variability in proto-planetary nebulae (PPN). Variability might arise due to binarity or pulsation. Many planetary nebulae display a bipolar shape, and it is suggested that this is caused by binarity. This can be investigated in PPN, particularly by radial velocity studies of those of spectral types F and G. Pulsation is known to exist in other types of post-AGB stars, and can be a means to learn more about the physical properties of the stars. No previous study of a sample of PPN has been published.