The malignant potential of 100 intraocular uveal melanomas was assessed by determining the mean of the ten largest nucleoli (MTLN). On a single standard microslide from each tumor, the maximum diameter of the ten largest nucleoli was measured using a manually operated micrometer. For comparison, three additional histopathologic parameters were determined for each case: Standard deviation of nucleolar area (SDNA), Callender cell type (CT), and largest tumor dimension (LTD). Of these four parameters, MTLN and SDNA were most highly correlated with death from ocular tumor. Furthermore, repeat measurement of all 100 cases revealed a level of reproducibility for MTLN similar to that for SDNA. Of greatest importance, the micrometer technique employed in this study has substantial cost and labor advantage over the computer-controlled system required to measure SDNA.