**title** Asp Conference Series, Vol. **volume**, **publication Year** **editors** the Autocorrelation Function of the Soft X-ray Background

The first positive detection of the X-ray background fluctuations at small angular scales is reported. ROSAT PSPC archive pointed observations are used to measure fluctuations at scales of 0. 03−0. 4. The pointings have been selected from an area free from galactic contamination. At separations below ∼ 0. 1 clusters of galaxies become a substantial source of the background fluctuations. The autocorrelation function of the fluctuations in the power law approximation has a slope of ∼ 1 for all the data but is substantially flatter (with slope of ∼ 0.7) when pointings containing bright clusters are removed. At separations 0. 3 − 0. 4 where the ACF estimates based on the ROSAT pointings and All-Sky Survey are available, both data sets give consistent results.