Pretreatment with pilocarpine hydrochloride has been demonstrated to increase the number of myofibroblasts in fistulized conjunctiva in rabbits. To determine if this observation is related to changes in the conjunctival vasculature that may be linked to pilocarpine, we evaluated the effects of a vasodilator and a vasoconstrictor in comparison with pilocarpine hydrochloride. Twenty Dutch-belted rabbits, with five rabbits per group, were treated in a masked fashion in both eyes with topical solutions of 4% pilocarpine hydrochloride, 0.3% papaverine, a combination of 4% pilocarpine and 2% epinephrine, or artificial tears for 3 months. Four of five rabbits in each group underwent thermal sclerostomies in both eyes; the fifth rabbit in each group served as a nonsurgical control. The mean number of myofibroblasts per high-power field was greater in the surgical eyes treated with pilocarpine (6.35 $pM 0.48) or papaverine (9.22 $pM 0.44) than in the eyes treated with both epinephrine and pilocarpine (4.80 $pM 0.70) or artificial tears (5.20 $pM 0.40). These results suggest that the vasoactive properties of topical agents can increase or limit the number of myofibroblasts following filtration surgery.