Solid tumors have the capacity to continuously stimulate the proliferation of new capillaries. Aliquots (0.1 cc) of aqueous humor were aspirated from the anterior chamber of the eye of 38 patients undergoing elective ophthalmologic surgery. The material was lyophilized and then inplanted on the chorioallantoic membrane (CAM) of 10-day-old chick embryos for bioassay. The angiogenesis capacity of each sample was graded as negative or positive. Nine of 10 patients with histologically proven retinoblastoma had positive vascular responses. Seven of 11 patients with choroidal malignant melanoma had a positive response to their aqueous humor on the CAM. Aqueous samples from eyes with an iris and ciliary body malignant melanoma and a metastatic breast carcinoma to the iris had a positive angiogenic response. By contrast, only one of 15 patients undergoing operation for cataracts, glaucoma, or other nonmalignant ocular disease showed an angiogenesis response. The one patient who a positive assay later developed lymphocytic leukemia. These studies show that certain intraocular tumors display angiogenesis capacity before clinically evident neovascular changes of floating tumor cells are seen. Patients without tumors showed no angiogenesis response.