Maintenance of hESC lines H1 and H9 in SR-bFGF conditions and differentiation in response to neutralization of bFGF. H1 (A,C,E) and H9 (B,D,F) hESC lines were cultured in MEF-CM (A-B), SR-bFGF media (C-D), or in the presence of bFGF neutralizing antibody (E-F). The H1 hESC line was maintained in SR-bFGF media for more than 6 passages to date (C) and H9 hESC lines for more than 31 passages to date (D). Addition of bFGF neutralization antibody to hESC lines cultured in MEF-CM induced differentiation and loss of colony integrity. Scale bars = 200 μm.