[en] The photometric behaviour of 21 Ap stars has been analyzed from observations obtained in the Geneva system. Variability has been detected for 9 Ap stars, as well as for a star which initially was a comparison star. Preliminary values for the periods are presented as well as an analytical description of the light curves. based on observations made at the Swiss telescope of the European Southern Observatory, La Silla, Chile. Complete Table 4 is available in electronic form at the CDS via anonymous ftp 18.104.22.168 or http://cdsweb.u-strasbg.fr/Abstract.html and full figures are accessible on the on-line version of the paper.