The extremely abrasive reinforcing phases present in metal matrix composites (MMCs) are known to dominate their machining behaviour. Consequently, the properties of the matrix material are often ignored. The work reported hen investigated the influence of matrix microstructure on the drilling performance of a 2618 aluminium alloy reinforced with 18% silicon carbide particles. The drills used were 8 mm diameter, titanium nitride coated K10 carbide with through-tool cooling. The workpiece material was drilled in four heat treatment conditions: as-extruded, solution treated and solution treated and aged for 12 and 20 hours. Drilling performance was assessed by measuring the wear on the drills, cutting forces, surface finish and the condition of the worn cutting edges. The results indicated that softer as-extruded and solution treated materials produced less wear and lower cutting forces than the harder aged materials. However, the height of the burrs produced during drilling were found to be greater with the softer materials and the quality of the drilled surface was also inferior. Examination of the worn cutting edges indicated that the wear mechanism was primarily one of abrasion although some attrition and edge chipping was also observed. It was concluded that when drilling these materials, the hear treatment condition of the matrix exerts a significant influence on machinability.