The anti-inflammatory properties of products that contain high levels of humic acid, such as peat, sapropeles, and mumie, are well described. The aim of this study was to establish the clinical efficacy of brown coal-derived potassium humate, as in vivo animal models had suggested similar efficacy of humate to prednisolone. In this double-blind, placebo-controlled study, atopic volunteers were recruited and randomized to placebo or 1.8 g potassium humate/day (three divided dosages) when they presented with hay fever. The efficacy parameters used were skin-prick tests for wheal and flare reactions, nasal smears for inflammatory cell accumulation, and cytokine levels. Patients also filled out daily symptom score cards to determine efficacy against symptoms of hay fever. Potassium humate resulted in a significant decrease in wheal and flare reactions as well as nasal eosinophil counts. These findings were supported by similar changes (not significant) in cytokine levels. Changes in symptom scores did not reach significance. This proof of concept study clearly demonstrated the potential of potassium humate in the treatment of inflammatory conditions such as hay fever. Drug Dev Res 71:358–363, 2010. © 2010 Wiley-Liss, Inc.