Monosodium urate (MSU) crystals were shown in synovial (SF) fluid taken from the asymptomatic knee joints of 11 out of 13 patients with tophaceous gout. Intracellular crystals were identified in some cases. Examination of synovial biopsies taken concurrently revealed MSU crystals in 2 out of 6 cases. The results show that MSU crystals can be found in SF and synovium in the absence of acute gout. This implies that additional factors are important in the pathogenesis of gouty inflammation.