Objective:To investigate the accuracy and precision of a recent‐generation reflectance photometer, Accu‐Chek III, for gestational diabetes mellitus screening with a single operator.Methods:Four hundred ten paired capillary and serum glucose samples collected prospectively were evaluated by a reflectance photometer and a glucose oxidase method (Beckman), respectively, during routine gestational diabetes mellitus screening with a single operator.Results:The mean Accu‐Chek III result was 12% greater than serum glucose oxidase (115.5 ± 1.4 and 103.4 ± 1.3 mg/dL, respectively). A serum glucose level of at least 135 mg/dL by glucose oxidase produced sensitivity and specificity of 0.81 and 0.68, respectively. At 155 mg/dL, the Accu‐Chek III sensitivity was 0.81 and specificity 0.74, and the method produced fewer false‐positive results (37 of 410 [9.0%] versus 41 of 410 [10%] than a 135‐mg/dL serum cutoff. Adjusting the Accu‐Chek III threshold by two times the coefficient of variation resulted in the same number of false positives as the Beckman technique at 135 mg/dL. The receiver operating characteristic curve cutoff for the venous value of 135 mg/dL was an Accu‐Chek III value of 141 mg/dL. Linear regression analysis predictedy= 20.6 + 0.919x,r= 0.838. The mean coefficient of variation was 3.9%.Conclusions:The Accu‐Chek III produced accurate and precise gestational diabetes mellitus screening results with a single operator. Because capillary blood is a combination of arterial and venous blood, an Accu‐Chek III cutoff of 155 mg/dL may be more appropriate for screening, considering the 10‐15% higher capillary glucose level in the fed state. An Accu‐Chek III cutoff of 155 mg/dL produced a higher specificity than venous serum at 135 mg/dL, with no decrease in sensitivity.(Obstet Gynecol 1994;83:1038‐42)