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Aims: We present accurate photometric time series of two Be stars: NW Ser andV1446 Aql. Both stars were observed at the Observatorio de Sierra Nevada(Granada) in July 2003 with an automatic four-channel Str\"omgren photometer.We also present a preliminary theoretical study showing that the periodicvariations exhibited by these stars can be due to pulsation.  Methods: An exhaustive Fourier analysis together with a least-square fittinghas been carried out on the time series for all four Str\"omgren bands. Severalindependent frequencies and non-periodic trends explain most of the variance. Atheoretical non-adiabatic code applied to stellar models for these stars showsthat g-modes are unstable.  Results: Both stars show rapid variations in amplitude, probably due to abeating phenomenon. Four significant frequencies have been detected for eachstar. Comparison of the observed amplitude ratios for each pulsationalfrequency with those calculated from theoretical pulsation codes allows us toestimate the pulsation modes associated with the different detectedfrequencies. NW Ser seems also to show unstable p-modes and thus could be oneof the newly discovered $\beta$ Cephei and SPB hybrid stars. Furtherspectroscopic observations are planned to study the stability of the detectedfrequencies.

Multiperiodic pulsations in the Be stars NW Ser and V1446 Aql