OBJECTIVE In this investigation the authors studied the effect of dapiprazole, an alpha-adrenergic blocking agent, on aqueous humor dynamics in patients affected with pigmentary glaucoma. METHODS Dapiprazole 0.5% eye drops were administered 3 times daily as adjunctive therapy to 16 pigmentary glaucoma patients in addition to timolol 0.5% eye drops twice daily. Computerized tonography was performed before and 3, 12 and 36 months after dapiprazole treatment. Sixteen sex- and age-matched pigmentary glaucoma patients treated with timolol 0.5% eye drops alone were used as a control group. RESULTS After 36 months of follow-up, the dapiprazole-treated group showed a significant increase in total outflow facility (C, from 0.17 +/- 0.04 to 0.22 +/- 0.07 ml min-1 mm Hg-1; p = 0.010, paired t test) and Po/C ratio (Q) significantly decreased from 113.39 +/- 31.02 to 89.22 +/- 51.66 (p = 0.036, paired t test). CONCLUSIONS Our results show that the introduction of dapiprazole in the therapy of pigmentary glaucoma may be useful in the long-term management of these patients. Its mechanism of action is likely to be due to iridoplegia; in fact, a decrease in the shedding of pigment occurs, with time, the outflow facility increases and the pigment clearance from the trabecular meshwork is enhanced.