The capillary blood glucose (CBG) estimated by some of the most frequent users of portable reflectance meters (PRMs) were assessed using blood applied to Whatman 31 ET filter paper at the time of the performance of the CBG. The performance of nursing staff on hospital wards, community groups screened for diabetes and patients exercising self monitoring of blood glucose (SMBG) at home were evaluated. The glucose was extracted from the filter paper with 5% trichloroacetic acid (TCA) and analyzed within 5 days of collection on a Technicon RA-1000 analyzer using Merck glucose dehydrogenase reagents. Of the 1255 samples collected, 385 were rejected due to inadequate sample collection, and a further 196 were rejected as they were received more than 5 days after collection, the time interval allowed for glucose stability on the filter paper. The CBGs obtained by the nursing staff were 2.2 - 17.1 mmol/l with a mean of 7.6 mmol/l; the community screened subjects CBGs were 1.5 -22.4 mmol/l with a mean of 5.2 mmol/l; and the SMBG users at home obtained CBGs of 1.0 - 15.1 mmol/l with a mean of 5.07 mmol/l. Of the 674 samples analyzed only 36.6% were within 10% of the laboratory blotting paper glucose (BPG) result. An alarming 35.8% exceeded 20% and 10.2% exceeded 50% of the BPG result. The correlation of all 3 groups with the BPG obtained by the laboratory were similar (correlation coefficient = 0.86, 0.85, 0.87 respectively).(ABSTRACT TRUNCATED AT 250 WORDS)