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The stress-rupture behavior of filamentary composites is of great concern in many long-term applications. We have begun a program to collect reliable stress-rupture data on very simple composites such as various fiber strands impregnated with an epoxy matrix. We de veloped a tensile test method for fibers, designed a stress-rupture test apparatus and verified its performance, and installed 400 test apparatuses in a controlled-environment building. This paper dis cusses the data collected to date on single-end S-glass/epoxy strands at three load levels: 83.8, 74.5, and 65.2% (based on the average breaking load). Using at least 100 specimens at each load level, we found that the time-to-break values consistently varied by a factor of 1000. The data clearly indicate a shorter life at higher loads. We are collecting data at three lower load levels: 50, 40, 33%. We are attempting to characterize the distribution function of the stress- rupture life but are not yet able to draw any conclusions.