In this presentation we show how the study of the isotropy of the X-ray sky contributes to our understanding of the structure of the universe at moderate redshifts (1≲z<<zrecombination). Actually, the anisotropy of the sky flux provides the information, much as the microwave sky anisotropy does for earlier epochs. [See reports in this volume.] Though we are currently unable to make measurements with the precision and small solid angles typically achieved in the microwave, comparatively crude

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... its from the X-ray fluctuations place limits on the largest scale structure of the universe. We first outline the measurements of the X-ray sky and its anisotropies made with the HEAO 1 A-2 experiment. Detailed presentations are found elsewhere [Shafer 1982; Marshall et al. 1980; Piccinotti et. al. 1982; Iwan et al. 1982; Shafer et al. in prep.]. We then show how the anisotropies place limits on the origin of the X-ray sky and on any large scale structure of the universe, following the example of previous analyses which used earlier anisotropy estimates [see e.g. Fabian and Rees 1978; Rees 1980; Fabian 1981].