The high-cycle stress-life (S-N) curve and fatigue crack growth threshold (ΔKth) behaviour of COMRAL-85TM, a 6061 aluminium-magnesium-silicon alloy reinforced with 20 vol.% Al2O3-based polycrystalline ceramic microspheres, and manufactured by a liquid metallurgy route, have been investigated for a stress ratio of R = -1 (fully reversed loading). Fatigue testing was conducted on both smooth round bar (S-N) specimens and notched round bar (fatigue threshold) specimens. Unreinforced Al 6061-T6 also processed by a liquid metallurgy route and six powder metallurgy processed composites with particle volume fractions ranging between 5% and 30% were also studied. S-N data revealed that the powder metallurgy processed composites generally gave longer fatigue lives than the matrix alloy, whereas COMRAL-85TM exhibited a reduced fatigue life. The fatigue threshold results were very similar for all the composites, being lower than for Al 6061-T6. Fatigue failure mechanisms were determined from examination of the fracture surfaces and the crack profiles. © 2008 Elsevier Ltd. All rights reserved.