The measurement of blood glucose using discs punched from dried spots on filter paper has been examined as a method to monitor patients' home blood glucose results. We confirm that the method is precise, reproducible, and accurate, but show that impregnation of the filter paper with boric acid leads to an initial false elevation in measured glucose levels and does not improve stability of the sample more than does refrigeration. Degradation of blood glucose is insignificant over 28 days if samples are stored at -20 degrees C, and samples kept at 4 degrees C show minimal falls provided they are analysed within 7 days. The greatest breakdown of glucose was shown to occur during the first 48 hours after application. The filter paper glucose measurements correlated closely with parallel measurements using a Yellow Springs Glucose Analyser.