The inability to precisely control pore morphology has limited investigations into the exact geometric requirements for optimum ingrowth of bone into porous ceramic implants. A laser machining technique was used to create regular arrays of tubular pores with opening diameters of 75 and 150 microns in sintered hydroxyapatite specimens. Scanning electron microscopy revealed that the size of pores produced in this way is highly reproducible. Heat from the laser beam appeared to produce a fused layer of material, approximately 6 microns thick, around each pore. The nature of this altered material was studied using x-ray diffractometry.