We investigated the analytical performance of fructosamine measurement in 33 routine clinical chemistry laboratories. We prepared 12 human control sera spanning a range of nondiabetic and diabetic fructosamine concentrations and assigned target values by using commercial reagents and a Cobas Bio centrifugal analyzer. Each control serum was analyzed by participating laboratories on two separate occasions. Averaged results were compared with target values, and systematic error was determined from slope and intercept regression coefficients. Overall, we found no significant (p greater than 0.05) slope or intercept bias, although slight nonlinearity was found with bichromatic instruments. Random error was determined from the standard error of estimate and from duplicate measurements. We found a median interlaboratory CV of 5.36% and similar analytical performance with all automated instruments used. The median random error with manual techniques was 18.1%. We conclude that fructosamine measurement as currently performed in routine laboratories is sufficiently accurate and reliable to function as an index of blood glucose control in diabetic patients.