Background: To evaluate the ability of topical ibopamine 2% to detect outflow resistance by comparing it with the tonography test in eyes with ocular hypertension (OHT). Methods: 62 eyes with OHT and 33 control eyes were included in this prospective study. Tonography was done manually as a standard outflow facility measurement. We used a C value of 0.18 mu l/min/ mm Hg or less and a P-o/C value of 100 and above as a positive tonographic test. The ibopamine test performed on the following day was considered positive if there was an intraocular pressure (IOP) change of at least 3 mm Hg. Results: The sensitivity of the tonography and ibopamine tests was 69 and 53%, respectively, in eyes with OHT. The specificity of both tests was 97%. Although the sensitivity of the tonography test is higher than that of the ibopamine test, the difference between both was not statistically significant in these eyes ( p = 0.409). Positive results in tonography were associated with higher IOP, while the results were not dependent on the IOP in the ibopamine test. Both tests together were positive in 33.87% ( 21 eyes) and negative in 11.29% ( 7 eyes) in 62 eyes with OHT. Conclusion: This study revealed that the ibopamine provocation test can detect outflow system resistance in eyes with OHT comparable with tonography which is a traditional outflow facility measurement. Ibopamine, however, can detect the eye with outflow impairment by a different and IOP-independent way, while tonography depends on IOP. Copyright (C) 2005 S. Karger AG, Basel.