  We analysed V-filter ASAS-3 photometry of 41 known Beta Cephei-type stars.
The ASAS-3 photometry was combined with the archival data, if available, to
determine long-term stability of periods and amplitudes of excited modes. We
detected amplitude changes in three Beta Cephei stars, BW Cru, V836 Cen, and
V348 Nor. Period changes were found in KK Vel and V836 Cen. Our analysis shows
that intrinsic period changes are more common among multiperiodic stars,
apparently because they are caused by some kind of mode interaction. In
addition, we found new modes for seven stars, and for ten others we provide new
solutions or remove ambiguities in the detected frequencies. One candidate
hybrid Beta Cephei/SPB star, HD133823, is discovered.
