Twenty-nine patients who had undergone enucleation for ocular malignant melanoma were studied. The results of the radioactive phosphorus uptake (32P) tests were correlated with histopathologic observations. There was a positive correlation between the 32P test results and the histologic degree of malignancy. Mixed cell melanomas were more frequent in the patients ranked with higher 32P test results. Spindle cell melanomas occurred more frequently in patients with lower 32P test results. Mitoses per field and degree of malignancy correlated positively with 32P test results when ranked in a masked manner by two ocular pathologists. Tumor volume and clinical factors did not correlate with the 32P test results. While patients with mixed cell melanomas had higher mean 32P test results than those with spindle cell melanomas, a large variance was noted. Because of this the 32P test is unreliable in predicting the histopathology of a tumor in individual cases.