Long-term regular observations for more than 10 years of 22 GHz 
maser
emission of the semiregular variable RT Vir have been carried out. The main
results are as follows:
1. A catalogue of 68 
O spectra of RT Vir is compiled.
2. The division of the spectrum of RT Vir into three parts is argued
and is related to the morphology of the source of the maser emission.
3. The integrated fluxes of the two parts of the spectrum
(
and 
) vary with
the same timescale of about 5-6 years.
4. Anticorrelation of the integrated fluxes of these parts of the spectrum, which may be due to alternating increasing of the intensity of the bipolar outflow, is observed.
5. The period of the maser activity in the RT Vir direction is much
longer than the average period of star variation.
Acknowledgements
We would like to thank the associates of the Radio Astronomical Station of the Lebedev Physical Institute for their help during the observations at the Pushchino RT-22 radio telescope and the Russian Foundation for Fundamental Research (Project Code 95-02-05087-a) for financial support.