We present the results of a systematic search for multiperiodic pulsators among the Galactic Bulge RR Lyrae stars of the OGLE-1 sample .
We identify one ” canonical ” double-mode variable ( RRd star ) pulsating in two radial modes .
In 38 stars we detect secondary periodicities very close to the primary pulsation frequency .
This type of multiperiodic variables constitute \sim 23 % of RRab and \sim 5 % of RRc population of the Bulge .
With the observed period ratios of 0.95 - 1.02 the secondary periods must correspond to nonradial modes of oscillation .
Their beating with the primary ( radial ) pulsation leads to a long-term amplitude and phase modulation , known as the Blazhko effect .
The Blazhko RRab variables occur more frequently in the Galactic Bulge than in the LMC .
The opposite tendency is seen in case of the RRd stars .
The differences of incidence rates are most likely caused by different metallicity of the two populations .
We discuss pulsation properties of the OGLE-1 Blazhko stars and compare them with predictions of theoretical models .
We argue , that the oblique magnetic pulsator model of Shibahashi ( [ 2000 ] ) can not account for the observations and should be ruled out .