In a prospective and randomised study, we compared the course of pulsed dye laser ab interno sclerostomy with the course of posterior lip sclerectomy in 25 rabbits. One eye of each rabbit was randomly selected to be treated with laser; the fellow eye underwent posterior lip sclerectomy. Intraocular pressure (IOP) determinations and slit lamp examinations were recorded pre-operatively, then every other day for 3 weeks on 21 of the rabbits. Histological examination was performed on the eyes of 3 randomly selected rabbits that were killed 72 hours post-operatively. Laser sclerostomy resulted in an average maximal drop in IOP of 9.5 mmHg on post-operative day 1, and posterior lip sclerectomy resulted in a similar drop of 10.5 mmHg (p = 0.43, t-test). By life-table analysis, 88% of eyes returned to within 2 mmHg of pre-operative IOP values within 7 days following either laser internal sclerostomy or posterior lip sclerectomy. There was no significant difference between laser internal sclerostomy and posterior lip sclerectomy eyes with respect to the number of days needed to return to within 2 mmHg of preoperative IOP values (p = 0.26, sign test of the life-table analysis). Pulsed dye laser internal sclerostomy appears to be as effective as posterior lip sclerectomy in lowering IOP in the rabbit model.