The transforming growth factor-βs are peptide growth factors known to play a central role in wound healing. Using a specific, in vitro assay of cell growth inhibition, we have detected transforming growth factor-β(TGF-β) in 24/24 aqueous humor specimens from eyes undergoing cataract extraction with intraocular lens implantation. The amount of TGF-βranged from 2.3 to 8.1 ng/ml (mean±SD = 4.5±1.7 ng/ml), with 61% present in the active form.Subtyping of TGF-βwas performed by addition of antibodies specific for theß1 andß2 isoforms to the growth inhibition assay, and confirmed with a sandwich enzyme-linked immunosorbent assay. None of the TGF-βdetected was of theß1 isoform; in contrast, theß2 isoform was present in every sample, implying that it might have originated from ocular tissues. The presence of this potent modulator of tissue repair in aqueous humor suggests a role in the healing processes following intraocular surgery, including glaucoma filtration surgery.