Serum pyridoxal and folate concentrations were measured in 518 diabetics. There were 185 males and 333 females. The level of pyridoxal was significantly lower in the diabetics when compared with 371 'healthy' controls and 25% had levels below the lower limit of the normal range. No significant difference was observed between diabetics being treated by diet alone, oral hypoglycaemics or insulin. Only 20 patients had a reduced serum folate level and in 6 this was accompanied by a low pyridoxal concentration. The results suggest that diabetics may have an increased demand for pyridoxal.