  We present the preparation for an observation of the Sunyaev-Zeldovich (SZ)
effect with the 100m telescope in Effelsberg. We calculate the expected
diminution of the cosmic microwave background radiation (CMB) at radio
wavelength towards a small sample of clusters of galaxies: A85, A665, and
Cl0016+16. We obtain the required parameters from the X-ray analysis of ROSAT
PSPC data of these clusters. We derive expected central diminutions \Delta
T_R,max of -(440\pm 180)\mu K for A665 and -(810\pm 680)\mu K for Cl0016+16.
For the cluster A85 we find evidence for a cooling flow. The best candidate for
a SZ measurement is the cluster 0016+16.
