Angiogenic factors were isolated by ion exchange chromatography from three established cell lines viz., HEp 2, HeLa and CHO, a primary culture of mouse mammary adenocarcinoma and from conditioned media of HEp2 and cultured mammary adenocarcinoma cells. The angiogenic activity was assayed by chicken chorioallantoic membrane assay. The angiogenic factor eluted at 0.5 M, exhibited lambda max at 258 +/- 1 nm, contained protein and nucleic acid. The cellular angiogenic factor showed a ratio of 1:1 for protein and nucleic acid whereas the secreted angiogenic factor had 3-5 parts of protein to 1 part of nucleic acid. The angiogenic factor from HEp2 and CHO cells did not bind to heparin-agarose. Microheterogeneity of the angiogenic factors was established by SDS-PAGE. Antiserum raised against the cellular angiogenic factor from HEp2 cells, showed a titre of 1:1600 by ELISA. The angiogenic factor was directly localized on whole cells by ELISA. Cellular as well as secreted angiogenic factors crossreacted with the antibody. Neutralizing effect of the antiserum on induction of angiogenesis was detected on chicken chorioallantoic membrane.