Clinical application of the laser flare-cell meter was described. The instrument was developed for concurrent quantitative determinations of the flare and number of cells in the aqueous humor. Diurnal variations were demonstrated in the aqueous flare, and also an increase in the flare with increasing age. The effects of drugs on aqueous humor dynamics were also studied. Orally administered 500 mg of carbonic anhydrase inhibitor reduced the aqueous humor formation by one-third. Concurrent study with the laser flare-cell meter and slit-lamp microscopy in uveitis cases has revealed that the former instrument is superior to the latter in making a quantitative evaluation of inflammation in the anterior segment of the eye. A follow-up study of postoperative inflammation was performed in patients undergoing extracapsular cataract extraction with posterior chamber intraocular lens implantation. Cases with uneventful postoperative course showed intense flare on the first postoperative day followed by a rapid decrease. Cases with inflammation and fibrin had high aqueous flare which showed an increase even before detection of fibrin in the aqueous by slit-lamp microscopy. Topical 0.5% indomethacin treatment was shown to be effective in suppressing the postoperative increase in aqueous flare but had little effect on cell count. In cases undergoing Argon laser trabeculoplasty, the aqueous flare in the treated eyes was determined to be significantly higher than that in the fellow eyes for four weeks postoperatively (P less than 0.05). The laser flare-cell meter has made it possible to determine the flare and number of cells in the aqueous humor quantitatively. This capability differentiates the instrument from the slit-lamp microscope as well as the instruments previously developed for similar purposes. The laser flare-cell meter is a newly developed useful tool to investigate the pathophysiology of the eye.