The in vivo glycaemic responses to six cereal-based foods traditionally consumed in South India were evaluated in patients with non-insulin-dependent diabetes mellitus (NIDDM) and healthy volunteers. All foods contained 50 g carbohydrate and were compared with a 50 g glucose load. Also studied were the in vitro starch digestibility and nutrient composition of the foods. The postprandial responses to the foods at 30, 60 and 120 min were significantly (P < 0·05) lower than those to the reference glucose, in both groups. The peak glucose responses for three foods, i.e. chapatti, idli and poori, occurred 60 min postprandially in both groups. The glycaemic index (GI) values ranged from 67 to 90 in NIDDM and from 44 to 69 in healthy subjects with no significant differences within the groups. Significant relationships were observed between peak responses and area under the curve for foods in patients with NIDDM and in vitro rate of starch hydrolysis (r 0·83, r 0·85, P < 0·05). The GI values predicted using in vitro data were found to be similar to the GI values observed in patients with NIDDM. The GI concept is useful for identifying foods in the habitual Indian diet with attributes of the desired glycaemic effect such as delayed peak rise and low area under the curve.