We have studied the relationship between serum glucose and urate in 260,699 men and 214,118 women from Sweden, and 140,084 men and 30,653 women from the UK. We found an increase in mean serum urate with increasing glucose concentrations up to 7.0 mmol/L in men and 9.0 mmol/L in women. Thereafter increasing glucose values were accompanied by a statistically significant decrease in urate concentrations. This fall was particularly marked in younger subjects. We believe this may have important implications for the free radical status of diabetics.