We evaluated in 7 eyes the mobility of a newly designed orbital implant made of hydroxyapatite. This orbital implant has a screw peg and is covered with a piece of sclera from the enucleated eye of the patient. The implant was well tolerated and there were no cases of proptosis during the follow-up of 1.8 +/- 0.6 years. Assuming the mobility of a healthy eye as 100%, photographic analysis showed the mobility of the anterior orbit to be 92.6% in adduction, 85.9% in abduction, 84.9% in supraduction, and 90.9% in infraduction. The mean tugging weight of the implant was, when measured by a strain gauge, 344.2 +/- 29.2 g in adduction and 327.6 +/- 33.4 g in abduction. These values corresponded to 90.4 +/- 4.4% and 89.5 +/- 5.3% respectively of those in a healthy eye. The presence of the orbital implant did not affect the electrooculogram as compared to a healthy eye. Cinematic studies using magnetic resonance imaging (MRI) showed that the constriction and extension of the extraocular muscles, which were sewn onto the orbital implant, matched that of a healthy eye.