Photometry of EP Lyrae and period changes in RV Tauri stars.

The RV Tauri variable EP Lyrae was observed between 1985 and 1992 in the UBV-system. The star, like AC Herculis, has a relatively regular light curve. Its period is rather stable during most of the observations, its current value is 83.46d EP Lyrae is classified as an RVB variable, i.e. its mean brightness is supposed to vary. It is shown that this classification is not correct, the mean brightness of the star is constant. The question of period changes in RV Tauri stars is discussed and a possible relation between colour and O-C amplitude is found. The difficulties with the usually assumed post-AGB evolutionary status of these variables are also highlighted.