Reactive hypoglycaemia (RH) is a condition that has been popularised in the media and lay literature, particularly that targeting women, over the past 30 years. The objective of the present study was to investigate whether a non-patient group reporting symptoms that they attributed to a low blood glucose level would demonstrate biochemical hypoglycaemia when symptomatic and whether their habitual diet and activity level differed from those of controls. Thirty non-obese, healthy women (aged 19–45 years) reporting symptoms more than once a week that they attributed to hypoglycaemia (RH group), and eighteen controls, measured their finger-prick blood glucose level 3h after breakfast and lunch, and recorded their diet and activity daily for 7d. The RH group also measured their blood glucose when symptoms were being experienced. Symptoms less than 4h after eating were classed as postprandial. The mean postprandial blood glucose level in the RH group when asymptomatic (4·66 (sem 0·08) mmol/l) was significantly lower than that of controls (5·05 (sem 0·11) mmol/l; P<0·01). Symptoms occurred 2·6 (sem 0·13) h after eating, at a lower blood glucose level (4·18 (sem 0·10) mmol/l; P<0·001) than when the women were asymptomatic. On symptomatic days, the RH group were more physically active than the controls (1·64 (sem 0·04) v. 1·50 (sem 0·03) multiples of resting energyexpenditure; P<0·05), with a lower energy intake (7901 (sem 311) et al.. 9332 (sem 227) kJ; P<0·001). In conclusion, subjects reporting symptoms they associated with hypoglycaemia generally did not demonstrate biochemical hypoglycaemia but did have significantly lower blood glucose levels than controls. Higher physical activity and a failure to match energy intake to estimated energy requirement may be important in the aetiology of symptoms.