PURPOSE: Laser flare photometry (LFP) is a new quantitative method for the evaluation of aqueous flare, making flare the only inflammatory parameter that can be evaluated precisely and objectively. The aim of this study was to characterize the inflammatory pattern of acute human leukocyte antigen-B27 (HLA-B27)-related anterior uveitis and to determine further clinical use and limitations of LFP in posterior inflammation. METHODS: In the first part of the study, 78 episodes of HLA-B27-related acute anterior uveitis were analyzed to determine mean pretreatment (initial) flare, mean flare evolution, need for additional periocular steroids, and mean duration of an episode. In the second part of the study, the use of LFP was further tested in posterior inflammation, first by analyzing the predictive value of a subclinical LFP-detected flare increase for disease recrudescence in posterior scleritis, and then by exploring clinical applications for LFP in posterior uveitis, where LFP was essential either in the establishment of a diagnosis or in guiding therapeutic decisions. RESULTS: Mean initial flare in HLA-B27-related acute anterior uveitis was 160 +/- 22 photons/msec, and mean duration of an episode was 18.5 +/- 15 days. A 50% and 90% flare reduction occurred after 2 and 8 days, respectively. In posterior scleritis, LFP was accurate in monitoring response to systemic steroid therapy and a small flare increase was predictive for disease recrudescence in five of six cases (predictive value 0.83, sensitivity 100%). In posterior uveitis, LFP was sensitive to monitor systemic treatments and to establish a diagnosis in unclear cases by measuring the effect of a selective therapy (therapeutic trial) on the flare level. CONCLUSION: In acute anterior HLA-B27-associated uveitis, LFP represented a potential improvement in management by allowing precise adjustment of therapy. In uveitis of the posterior segment, our data confirm the validity of LFP to monitor response and adjust systemic therapy and to detect disease recurrence in patients with a sufficient pretreatment level of associated blood-aqueous barrier disruption (flare).