Macrophages play an important role in proliferative vitreoretinopathy (PVR). Since macrophage maturation may be modulated by the local microenvironment, we determined the effect of retinal pigment epithelium (RPE) cells interacting with monocytes on macrophage maturation. The enriched monocyte fraction of peripheral blood mononuclear cells was cocultured with RPE cells. Cell-free supernatants conditioned during the culture periods 0-4 days (growing RPE cells) and 4-8 days (confluent RPE cells) were tested for their capacity to induce monocyte/macrophage differentiation of the promyelocytic cell line HL-60, which was measured by the expression of CD11c and CD14 and flow cytometry. RPE cells released factors that increased the CD14 expression on HL-60 cells in terms of percentage of positive cells (22.7% vs. control 10.4%). RPE-cell-conditioned supernatants had no effect on the CD11c expression. Monocytes secreted substances that increased the expression of CD11c (20.5% vs. control 9.1%; p = 0.003) and CD14 (31.6% vs. control 10.4%; p < 0.0001). Supernatants from cocultures increased the CD11c (19.8%) and CD14 expression (40.8%) to values that were similar to the sum of those of cell monocultures. Supernatants conditioned during the later culture had no effect on CD14 and CD11c expression. We conclude that invading monocytes and RPE cells could create an intraocular microenvironment that supports macrophage maturation during the initial stage of PVR.