The self-selected diet of 16 subjects with noninsulin- dependent diabetes mellitus (NIDDM) was supplemented for 6 mo with either a granolalike bar containing 35.5 g carbohydrate and 6.6 g guar gum/bar or a placebo bar containing carbohydrate but no guar gum. Subjects consumed a mean of 4.8 bars/day. Average guar gum consumption at the end of the study was 31.7 g/day. One week before and at the end of the study, subjects were admitted to a metabolic ward and fed a controlled diet similar to their self-selected diet. Food, feces, and urine were composited for analysis of iron, zinc, copper, calcium, magnesium, and manganese. Eight subjects consuming the guar gum supplement and 6 subjects consuming the placebo bar completed collections for mineral balance. Neither consumption of guar gum nor placebo bar significantly changed apparent mineral balance for iron, copper, zinc, calcium, manganese, or magnesium from prestudy levels to 6-mo levels, and no significant differences were observed between the two groups. With the exception of copper, men consumed significantly more minerals than women. We conclude that consumption of guar gum by patients with NIDDM does not adversely affect apparent mineral balance.