Clinical imaging approaches to detect inflammatory biomarkers, such as cyclooxygenase-2 (COX-2), may facilitate the diagnosis and therapy of inflammatory diseases. To this end, we report the discovery of N-[(rhodamin-X-yl)but-4-yl]-2-[1-(4-chlorobenzoyl)-5-methoxy-2-methyl-1H-indol-3-yl]acetamide chloride salt (fluorocoxib D), a hydrophilic analog of fluorocoxib A. Fluorocoxib D inhibits COX-2 selectively in purified enzyme preparations and cells. It exhibits adequate photophysical properties to enable detection of COX-2 in intact cells, in a mouse model of carrageenan-induced acute footpad inflammation and inflammation in a mouse model of osteoarthritis. COX-2-selectivity was verified either by blocking the enzyme's active site with celecoxib or by molecular imaging with nontargeted 5-carboxy-X-rhodamine dye. These data indicate that fluorocoxib D is an ideal candidate for early detection of inflammatory or neoplastic lesions expressing elevated levels of COX-2.