Synovial fluid (SF) samples, all containing monosodium urate crystals, obtained from 18 asymptomatic knees of 12 patients with gout, were serially analyzed before and one month after treatment with 1 mg/day of oral colchicine. Before treatment, the SF contained 612 [confidence limits (CL) = 282, 942] cells/mm3, while after treatment these values decreased to 274 (CL = 73, 471) cells/mm3 (p less than 0.005). In all cases, pretreatment cell counts were higher than the corresponding posttreatment values. The percentage of polymorphonuclear leukocytes also diminished from a pretreatment value of 13.0 (CL = 7, 19) to 4.5 (CL = 2, 7) after colchicine administration (p less than 0.005). These results strongly suggest the presence of baseline subclinical joint inflammation which is reduced by colchicine. The preventive effect of this drug on the occurrence of new attacks may relate to its effect in reducing the baseline inflammation of the asymptomatic joints.