In 96 patients with uveal malignant melanomas the tumours were investigated by DNA flow cytometry. Thirty-eight per cent of the melanomas were aneuploid. By univariate analysis significant correlations with survival were found for histological type, tumour size, DNA ploidy, evidence of 'blind eye' and S-phase fraction. By multivariate analysis, significant prognostic variables were found to be histological type (P = 0.0008), tumour size (P < 0.0001) and DNA ploidy (P = 0.0038). Evidence of 'blind eye' was not significantly correlated with survival after adjustments for the other variables mentioned above. The S-phase fraction could be estimated in all 60 diploid tumours and in 12 of 36 aneuploid melanomas. By univariate analysis this variable was found to be a significant prognostic factor, but did not remain so after adjustment for ploidy, histological type and tumor size. We further conclude that patients with small DNA diploid uveal melanomas of spindle cell type have a rather favourable prognosis.