A bioassay that measures the potency of the FGF-4 transgene carried by a replication incompetent adenovirus type 5, Ad5FGF-4, was developed on ARPE-19 cells. The assay is carried out in a microtiter plate format and measures cellular proliferation following infection of ARPE-19 cells with a serial dilution of Ad5FGF-4. Proliferation is measured as a percentage increase in absorbance reading in relation to a mock-infected control. Ad5LacZ and Ad5FGF-4 viruses treated similarly to the test sample are included as negative and positive controls, respectively. The increased absorbance reading resulting from infection with the virus correlates with FGF-4 production as determined by an FGF-4 enzyme-linked immunosorbent assay, an increase in de novo DNA synthesis as measured by BrdU incorporation, and an increase in the total cell number. The assay shows a dose-dependent response and is capable of evaluating the stability of Ad5FGF-4. A sample being tested is compared with a reference standard, and the relative potency value is obtained by a parallel line analysis of the dose-response curve of the test article in relation to the reference standard. Therefore, this procedure can be used as an in vitro efficacy-indicating assay, demonstrating that the FGF-4 transgene product carried by Ad5FGF-4 is biologically active.