The scatter in the failure strain, load and stress of high-tenacity polyester and aramid yarns is studied experimentally. From the data, the failure strains of polyester and aramid yarns can be fitted to a two-parameter Weibull distribution. However, the log-log dependence of the strain on the gauge length is best represented by the Watson-Smith modification. Whereas the strengths of polyester yarns are best described by the two-parameter Weibull distribution, those of aramid yarns are best represented by the Gumbel distribution. The effect of strain rate on the strength distribution of aramid yarns is also examined. The strength of aramid yarns decreases slightly with an increase in the strain rate. This is contrary to theoretical predictions but in line with other test data.