OPTICAL AND X-RAY STUDY OF MS1603+2600

We present results from similar to 2 years of optical monitoring of an unusual interacting compact binary MS1603+2600 together with the resu lts of ROSAT observations. Our CCD-photometry confirms the erratic beh aviour of the optical light curve shape reported by Morris et al.(1990 ). The ROSAT-PSPC observations suggest that MS1603 might be a short pe riod soft X-ray transient (SXT) never seen in outburst. This would pro bably require, that the compact object in MS1603 is a black hole rathe r than a neutron star. In addition to optical photometry and ROSAT dat a, we present first circular polarimetric observations of the source a nd discuss the nature and origin of MS1603+2600.