In order to avoid the factors of the corneal barrier and tearing washout on absorption of eye drops, dopamine and antagonists were injected into rabbit eyeballs through vortex veins. Many dopamine antagonists, such as haloperidol, moperone, metoclopramide, trifluperidol, lenperone, and fluoropipamide, lowered the intraocular pressure (IOP), whereas a few of them, such as chlofluperol and trifluoperazine, raised the IOP. Furthermore, it was found that dopamine agonists also could either increase or decrease the IOP. The ocular hypertensive effect of dopamine was blocked by haloperidol as expected. However, when the hypotension-inducing dopamine agonist, bromocriptine, and antagonist, haloperidol, were combined, the IOP remained unchanged. It was concluded that dopamine agonists and antagonists act at different sites and changes in IOP resulted from a combined summary of these complex effects. As a result, dopamine agonists and antagonists, while they may both lower the IOP when given alone, can antagonize each other through different sites and produce no net change in IOP.