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We have monitored the radial velocity variability in a number of proto-planetary nebulae (PPN) over the past 3 years. Observations were made with the radial velocity spectrometer at the DAO, and have a precision of 0.5 km/s. Radial velocity variability can arise from binary motion or pulsation in these post-AGB objects. The demonstration of a binary nature for some of these objects can have important implications for the understanding of their physical properties, and for the shaping of their circumstellar shells. We report the following preliminary results: all 9 well-studied PPN show variability, with peak-to-peak amplitudes ranging from 5 to 13 km/s; 4 objects clearly display periodic variations, with periods ranging from 95 to 340 days.
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