Postmortem explants of human trabecular meshwork from 23 eyebank eyes had a growth rate of 32% (71/160) cultures, with 8% (12) showing abundant cellular spread. The confluency achieved with eyes from donors of 11-40 yr of age was 100%. One of the cultures grew profusely and was studied through 8 passages in culture. This culture had the morphologic characteristics described by Polansky et al. for cultured human trabecular meshwork cells. A sensitive radioimmunoassay for fibronectin in tissue culture supernatant showed an increase in fibronectin secretion over a 96 h period, with a characteristic shift-down response occurring between 24 and 48 h postmedia change. Of 4 cultures, 3 showed the presence of laminin, a basement membrane protein, establishing that the cells are not fibroblasts.