A procedure for the quantitation of non-enzymatically glycated apolipoprotein A1 (GApoA1) was developed and optimized. Glycated total protein was separated from plasma using m-aminophenyl-boronate affinity chromatography. Apolipoprotein A1 present in the glycated and non-glycated fractions of each sample was determined by rate nephelometry, and the percent glycated apo A1 calculated. The measuring range of the assay was 0.5-8.0% GApoA1. The within- and between-run CV's were less than 5.2 and 7.9%, respectively, and recoveries were greater than 92%. Free glucose did not affect the results. In a group of female non-insulin diabetic subjects the mean GApoA1 was 3.8 +/- 1.6% (mean +/- SD). In non-diabetic subjects the mean level of GApoA1 was 2.1 +/- 0.8% (mean +/- SD).