Fifty-six ocular hypertension (OHT) patients were examined for 2-3 days in the Eye Clinic of Kuopio University Hospital. No glaucomatous changes were found. Twenty-seven of them were found to have several risk factors for developing glaucoma and medication was started. Twenty-nine of the patients did not show risk factors and had no medication. Color vision was examined with the Farnsworth-Munsell 100 (FM 100) hue test and Besançon anomalometer, later Color Vision Meter 712 at the beginning of the study and 3 years later. None of the 56 patients showed any glaucomatous changes after 3 years of the study. In the treatment group, the FM 100 test showed significantly (paired t-test, p = 0.004) improved error scores after 3 years. In the non-treatment group, 19 patients did not develop risk factors; they had no significant changes in the color vision results. In 10 patients of the non-treatment group, risk factors had developed with elevated intraocular pressure and medication was started for them after 3 years. Their color vision results in the blue anomalous quotient (AQ) of the anomalometer had significantly shifted to the blue part of the equation (paired t-test, p = 0.04). The other color vision results had not changed significantly. The significantly improved FM 100 scores in the treatment group could mean, that the treatment has a beneficial effect for the OHT eyes at risk for developing glaucoma.(ABSTRACT TRUNCATED AT 250 WORDS)