Uveal melanoma, although a comparatively rare tumour of man, is the commonest malignant tumour of the eye. The tumours can be composed of varying cell types; pure spindle, pure epithelioid and a mixture of spindle and epithelioid cells, with a worse prognosis being associated with the pure epithelioid cells. Fow cytometry is a modem method of studying cell surface marker expression which makes use of fluorescently labelled antibodies specific for these molecules. It gives quantitative analysis of a large number of cells from a substantial section of the sample in a short period of time and allows small changes in fluorescence to be quantified.