The falling success rate of ALT (Argon Laser Trabeculoplasty) has raised the interest in some new laser techniques, such as q-switched Nd:YAG laser trabeculoplasty (Coherent Selecta 7000). The "selective" laser trabeculoplasty destroys melanosomes of pigmented trabecular meshwork cells, sparing adjacent non-pigmented cells and tissues. Our goal was to establish the IOP lowering effect of selective laser trabeculoplasty (SLT--Selecta Laser Trabeculoplasty) in comparison with ALT. We have examined 27 patients (10 men, 17 women) aged 35-82, with open angle glaucoma and visual field deterioration despite maximal tolerated topical therapy (21 patients--POAG, 3--NPG, 1--pigmentary glaucoma, 1--pseudoexfoliative glaucoma, 1--juvenile glaucoma). One eye of each patient was randomly chosen for SLT, the other eye underwent ALT. In each method 50 burns were applied in 180 degrees angle with power settings of 600-1000 mW for ALT and energy settings of 0.5-1.4 mJ for SLT. The IOP was measured 1 hour before laser treatment and 1, 2, 24 hours and 3 months after treatment. The mean initial IOP in eyes selected for SLT was significantly higher (21.26 +/- 4.82 mm Hg) than in eyes selected for ALT (20.26 +/- 4.01 mm Hg), t-test: p = 0.037. However, there was no statistically significant difference in the IOP lowering effect between eyes treated with SLT and eyes treated with ALT. The mean IOP drop from the pre-treatment values was -2.85 +/- 4.62 mm Hg after SLT and -2.63 +/- 3.60 mm Hg after ALT (t-test, p = 0.84). All values: 2, 24-hours and 3 months after treatment were significantly lower than pre-treatment values in both groups (t-test, p < 0.03). Only in the 1st hour after SLT the IOP drop was not significant. There was a significant correlation between the amount of pigment on the trabecular meshwork and the IOP fall (U Mann-Whitney test). In SLT group 6 patients (21%) developed mild iritis during 1st day after laser treatment, which disappeared after fluorometholon drop therapy. Both methods--SLT and ALT--have equivalent IOP lowering effect in short time observation (3 months). Due to entirely novel mode of Selecta laser action, long term results may show significant differences.