We aspirated synovial fluid from the knees of 50 patients with asymptomatic, nontophaceous gout, in whom synovial fluid monosodium urate (MSU) crystals had previously been documented in the knees or other joints. Fifty-eight percent of these asymptomatic patients had MSU crystals in their knee joints. Serum uric acid levels, serum creatinine levels, volume of synovial fluid aspirated, and cell counts of the aspirated fluid did not differentiate the MSU crystal-positive group from the group without MSU crystals. Clinical factors such as alcohol abuse, coronary heart disease, hypertension, duration of gout, duration of the intercritical period, and drug therapy did not differentiate the 2 groups. Nineteen patients consented to aspiration of their other knee. Seven of these patients (37%) had MSU crystals bilaterally, and 6 patients (32%) had them unilaterally. The implications of the persistence of MSU crystals (including those in intracellular locations) in many patients, despite normalization of serum uric acid levels, should be determined. Knee joint aspiration is a sensitive method for the demonstration of MSU crystals in asymptomatic patients. The procedure might also be useful in documenting these crystals in patients who have had attacks of arthritis with features consistent with a diagnosis of gout, but in whom MSU crystals have not been documented.