Seventy six subjects (63 females and 13 males) with an average age of 50.5 years, all of them with familial and/or obstetric history for diabetes mellitus, were submitted to glucose tolerance tests with oral glucose challenges of 50 and 100 g. The tests were all analysed by different criteria of current usage in medical literature (Wilkerson, Fajans and Conn, British Diabetes Association and University Group Diabetes Program). We concluded that the 100 g glucose challenge gives a greater index of positivity by all the criteria above referred when compared to 50 g challenge. Wilkerson's criteria is less sensitive than the others, when applied to 100 g glucose challenges.