Insulin-dependent diabetes mellitus is associated with an increased frequency of certain histocompatibility antigens located on chromosome six, the most common types being B-8, B-15, DR-3, DR-4, and DR-7. We therefore theorized that screening for these subtypes may allow the identification of those women with gestational diabetes who will remain euglycemic on dietary modification (class A1) compared with those who will require insulin to achieve euglycemia (class GB). From 1982 to 1987, 228 black women with gestational diabetes were screened for the above histocompatibility antigens. As theorized, certain histocompatibility antigen subtypes were more common in women with class GB gestational diabetes mellitus; DR-2 (41.8% versus 23.7% p = 0.015), B-15 (p = 0.07), and DR-3 (p = 0.08). However, because of the low sensitivity (42%), specificity (75%), and positive predictive value (36%), this test is impractical in the clinical management of women with gestational diabetes mellitus. © 1991, by Thieme Medical Publishers, Inc. All rights reserved.