Type 2 diabetes is commoner in Asians than Caucasians. Many nitrosamines are diabetogenic, causing both type 2 and type 1 diabetes. Of CD1 mice fed with betel-nut or associated nitrosamines 8·5 % develop glucose intolerance with marked obesity. Glycaemia and anthropometric risk markers for type 2 diabetes were therefore examined in relation to betel usage in 993 ‘healthy’ Bangladeshis by one bilingual research-worker (N.M.). Of these, 12 % had known diabetes. A further 145 of 187 subjects ‘at-risk’ of diabetes (spot glucose >6·5 mmol/l <2 h after food, or >4·5 mmol/l >2 h after food) had a second blood glucose sample taken; sixty-one were confirmed as ‘at-risk’, and had an oral glucose tolerance test; nine new diabetics were identified. Multiple regression analysis showed that spot blood glucose values decreased with time after eating (P = 0·0005) and increased independently with waist size (P = 0·0005) and age (P = 0·0005) without relationships to other aspects of the diet, season or smoking. Waist size was strongly related to betel usage independent of other factors such as age. Betel use interacted with sex, relating to increasing glycaemia only in females. Since waist and age were the major markers of increasing glycaemia we suggest that betel chewing, a habit common to about 10 % of the world population (more than 200 million people) may contribute to the risk of developing type 2 diabetes mellitus.