  We present results of a long-term variability campaign on the Seyfert 1
galaxy Markarian 110. Mkn 110 is a narrow-line Seyfert 1 object hosted in a
morphological peculiar galaxy. We monitored the optical continuum and the line
intensities as well as their profiles over a time interval of nearly ten years.
The continuum and the Balmer lines varied by a factor of 2 to 5 within two
years. The HeII4686 line showed exceptional intensity variations of a factor of
eight. We detected an additional independent very broad-line region in high
intensity stages of the Balmer and HeII lines. The CCF analysis of the HeII
line indicates that this very broad-line region originates at a distance of 9
light days only from the central ionizing source.

Astrophysics