Measurement of glycated proteins can be of use in diagnosis and monitoring of diabetic dogs. Its use in monitoring can be facilitated by comparison of results with a reference interval derived from levels in normal dogs. In this study, a commercial immunoturbidometric assay was used to measure glycosylated haemoglobin in 15 normal dogs over a 5-week period. Following statistical analysis of the results a critical difference value of 0.38 per cent was obtained.