Abstract. A low angle scatter instrument (LASI) has been designed and built at Montana State University under contract to the Los Alamos National Labora-tory. The instrument is capable of measuring scatter at 0.1 ° from the specular beam on most samples and at 0.01 on high scatter samples. Samples may be either reflective or transmissive components. LASI consists of a small aperture detector (100 Am nominal) that is scanned through a focused beam under computer control. The system measures light intensity over approximately nine orders of magnitude. Because the instrument produces some scatter, scans are made with and without the sample present. Following a normalization process, the two data sets are compared to determine the scatter due to the sample alone. Extensive software is used to control the data-taking process, analyze the data, and present the results in graphical form. In this paper a review of the instrument is presented, rather than an extensive survey of scattering data. The basic design problems involved in making these types of instruments are discussed, and procedures for taking measurements are given. We conclude that the major constraint on this type of measurement is scatter from the instrument itself. The difficulties involved in obtaining optics with small amounts of low angle scatter emphasize the need for this type of instrumentation.