Computer-based image analysis offers a wide range of techniques which can be used to make objective and reproducible detection and measurement of subvisual features of microscopic images of cells. We describe here a prototype imaging system for specimen analysis. Using this system, studies have been carried out on the low metastasis variant F1 and high metastasis variant BL6 of the B16 murine melanoma. Cell cycle analyses have been carried out based on the measurement of integrated nuclear density, nuclear area and nucleocytoplasmic ratio of cells stained using standard procedures. It has been possible to discriminate between the two cell populations on the basis of ploidy. The two cell lines had a similar proportion of cells in the S-phase.