Ultrasmall‐angle x‐ray scattering (USAXS) using the Bonse–Hart twin‐crystal diffractometer system1on a synchrotron radiation source (SRS) is being developed as a technique for studying the structure of colloidal dispersions and other inhomogeneous materials with features in the size range 500 A˚ to 1 &mgr;m. The use of well‐characterized colloidal samples in this range highlights the problems which must be resolved in order to obtain reliable data from the system. This paper addresses the specific problems of attenuation, absorption, detector dead time, and smearing for the USAXS configuration. The system has been used to study a variety of materials and some previously unobserved features have been found in the scattering profile of a colloidal latex. This serves to indicate the value of the improved system in the field of colloidal science.