Objective - To identify a technique for measurement of glycated hemoglobin percentage in blood samples obtained from various species of nonhuman primates (NHPs), to determine whether these percentages varied with respect to glycemic control, and to assess whether this physiologic variable provided a suitable test for diagnosing diabetes mellitus in NHPs. Sample Population - 166 blood samples collected from 121 NHPs comprising 22 species from the Haplorhine and Strepsirhine suborders and including nondiabetic, treated-diabetic, and diabetic animals in 23 zoologic institutions throughout the United States. Procedure - Hemoglobin A1c percentage was measured in 154 samples by use of high-performance liquid chromatography. Total glycated hemoglobin percentage was measured in 159 samples by use of a boronate-affinity chromatographic assay. Glucose concentration was measured in 157 samples with an autochemical analyzer by use of a hexose kinase method. Results - The boronate-affinity chromatographic technique for measurement of total glycated hemoglobin percentage was the most suitable method. Nondiabetic Haplorhines had percentages higher than those in nondiabetic Strepsirhines. In Haplorhines, diabetic animals had percentages higher than those in treated-diabetic animals, which had percentages higher than those in nondiabetic animals. In Strepsirhines, this pattern was less pronounced. Conclusions and Clinical Relevance - Measurement of total glycated hemoglobin percentage provides useful information for diagnosing diabetes mellitus in Haplorhines and, possibly, in Strepsirhines. Until reference ranges are established for each species, it is recommended that results for samples from NHPs without clinical signs of diabetes mellitus be compared with results of samples collected concomitantly from NHPs with clinical signs of this condition.