The effects of gauge length and test speed on the tenacity and strain of sisal aggregates (Agava sisalana) were determined. Tenacity was generally higher with shorter gauge lengths and slower test speeds. Strain was higher with shorter gauge lengths. However, the effect of test speed on both tenacity and strain was not the same at every gauge length. The mode of fibre failure appeared to differ with the test conditions. Longer specimens and those tested at faster speeds were prone to higher levels of longitudinal splitting. The effects of different ageing regimes on tenacity and strain of sisal aggregates were also determined. Tenacity was affected by elevated temperature and UV; strain by UV and simulated natural ageing. (c) 2006 Springer Science + Business Media, Inc.