The benefits of self-monitoring of blood glucose (SMBG) were assessed in 38 Chinese adults on conventional insulin regimens who had been performing SMBG for a mean duration of 26 months (range 15-40). For analysis patients were divided into 2 groups. Group A consisted of 27 insulin-requiring patients who were referred for SMBG because of poor control or young age (less than or equal to 35 years). Group B consisted of 11 IDDM patients who were on SMBG from diagnosis. Mean age and duration of SMBG were similar in the 2 groups though group A had longer duration of disease. In group A, mean haemoglobin A1 (HbA1) decreased from 12.4 +/- 0.5% before SMBG to 10.9 +/- 0.5% at 6 months (P less than 0.005), 10.7 +/- 0.5% at 12 months (P less than 0.005) and 10.3 +/- 0.4% after long-term SMBG. This was accompanied by a significant reduction in insulin requirement from 0.82 +/- 0.07 U/kg/day to 0.72 +/- 0.07 U/kg/day (P less than 0.05). In group B, insulin requirement progressively decreased in the first 6 months. At 12 months, mean HbA1 was 9.0 +/- 0.5% and insulin requirement was 0.58 +/- 0.08 U/kg/day. No significant change in HbA1 or insulin requirement was observed beyond the first year. After long-term SMBG, 82% of patients in group B had good control (HbA1 less than or equal to 10%) compared to 45% only in group A (P less than 0.05). Long-term SMBG is associated with sustained improvement in diabetic control and is particularly beneficial if introduced to diabetic patients right from diagnosis.