Ultrasonography was performed in 24 eyes harboring malignant melanomas of the choroid to study tumor regression after xenon-arc photocoagulation at periodic intervals after each photocoagulation session. Ophthalmoscopically, 20 (83%) eyes revealed a complete regression of the tumor after 3 months to 3 years of treatment. However, ultrasonography revealed complete tumor regression in only 13 (65%) out of these 20 eyes while the remaining 7 (35%) 9 eyes had a residual tumor prominence of 0.75-1 microsecond. 14 (70%) out of 20 tumors were completely regressed 1 year after photocoagulation treatment. Most of the eyes revealed complete disappearance of the tumor after 3-5 photocoagulation sessions. Though 4 tumors which did not respond to photocoagulation treatment were located in the central temporal retina within the vascular arcade, no statistically significant difference could be seen between tumor regression and location of the tumor. Complete tumor regression was seen in 4 out of 5 eyes after encircling coagulation alone while 16 out of 19 eyes revealed complete tumor regression after addition of direct treatment of the tumor. Photocoagulation appeared to be a useful tool in the treatment of small choroidal melanomas.