Familial Mediterranean fever (FMF) is characterised by recurrent fever and serositis. The most important complication of the disease is amyloidosis. Cheap and non-invasive methods would be important in predicting or establishing the early diagnosis of amyloidosis. For this purpose, we studied the role of urinary glycosaminoglycans (GAG). The study group included 123 FMF patients without an attack and 11 patients with FMF associated amyloidosis. Ten healthy children and ten patients with primary nephrotic syndrome served as controls. In patients with amyloidosis, urinary GAG were, lower than in patients with FMF, patients with nephrotic syndrome and controls (median and range: 8.54 mg hexuronic acid/g creatinine (1.87-25.5), 5.8 (1.7-17.26), 23.12 (8.74-28.06) and 19.25 (14.2-26.9) respectively, P < 0.01). There was a significant negative correlation between the duration of the disease and urinary GAG (r = -043, P = 0.002). In 49 FMF patients with a low GAG, urinary GAG increased significantly after an increase in the colchicine dose (median and range: 6.64 mg hexuronic acid/g creatinine (1.77-19.39) and 9.45 mg hexuronic acid/g creatinine (2.36-28.9), P < 0.01). Conclusion: These results suggest that urinary glycosaminoglycan levels may be a predictor of amyloidosis in patients with familial Mediterranean fever. We also suggest that effective colchicine doses may be monitored by following urinary glycosaminoglycan excretion.