It appears justifiable to regard the finding of urate crystals in synovial fluid as pathognomonic of acute gouty arthritis. In a study conducted by the author, urate crystals in the synovial fluid of 10 of 12 patients with clinically suspected gouty arthritis were identified by polarized light microscopy and uricase digestion. This procedure also excluded the disease in 53 patients and established its presence in three patients in whom the diagnosis had been missed clinically. Fluid containing crystals was obtained most frequently from the knee, bunion joint and ankle, in that order. Most identifications were made on fluids aspirated from the site of an acute attack.