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Results of the long-term (11 years, from 1996 to 2006) H$\alpha$ and H$\beta$line variations of the active galactic nucleus of NGC 4151 are presented. Highquality spectra (S/N>50 and R~8A) of H$\alpha$ and H$\beta$ were investigated.We analyzed line profile variations during monitoring period. Comparing theline profiles of H$\alpha$ and H$\beta$, we studied different details (bumps,absorption features) in the line profiles. The variations of the differentH$\alpha$ and H$\beta$ line profile segments have been investigated. Also, weanalyzed the Balmer decrement for whole line and for line segments. We foundthat the line profiles were strongly changing during the monitoring period,showing blue and red asymmetries. This indicates a complex BLR geometry of NGC4151 with, at least, three kinematically distinct regions: one that contributesto the blue line wing, one to the line core and one to the red line wing. Suchvariation can be caused by an accelerating outflow starting very close to theblack hole, where the red part may come from the region {closer to the blackhole than the blue part, which is coming} from the region having the highestoutflow velocities. Taking into account the fact that the BLR of NGC 4151 has acomplex geometry (probably affected by an outflow) and that a portion of thebroad line emission seems to have not a pure photoionization origin, one canask the question whether the study of the BLR by reverberation mapping may bevalid in the case of this galaxy.

Long-term variability of the optical spectra of NGC 4151: II. Evolution of the broad Ha and Hb emission-line profiles