Forty-nine male rats were divided into seven groups of seven rats for a two month study of the effects of chronic Cr 3 + and As 3 + consumption on glucose tolerance. Five groups received organic or inorganic Cr 3 + and/or As 3 + in their drinking water, one group was fed a special Cr-free diet and the control group was fed the same feed as the first five groups and distilled water ad libitum. Glucose tolerance and insulin levels were determined at two months. The parameter total blood glucose concentration TBGC, which was based on basal glucose, glucose curve displacement with respect to the control curve, time of the maximum blood glucose concentration and the area under the curve, was used to assess the data. The Cr 3 + groups presented contrasting effects depending on whether they had received organic or inorganic Cr 3 + and of the presence of As 3 + . The effect of organic Cr 3 + alone was hyperglycemic, while the effect of the inorganic Cr 3 + alone was hypoglycemic. The effects of the As 3 + alone and of the Cr-free diet were also hypoglycemic.