The objective of this study was to identify individuals of the same age, sex, activity level and fat-free mass who differed in their level of energy intake (EI). Estimates of energy intake and physical activity level were derived from three-day food and activity records from 430 individuals 17-54 years of age. Body composition was measured by underwater weighing and body fat and fat-free mass were obtained. Subjects were grouped into four categories based on age and sex (females aged 17-34 and 35-54 years and males aged 17-34 and 35-54 years). Subjects were identified as small eaters (SE) or large eaters (LE) according to kJ of EI per kg body weight, SE being from the lower quartile and LE from the upper quartile of their distributions. The results showed that, on average, LE consumed almost twice as many kJ per kg body weight as SE (about 200 versus 100). In addition middle-aged male and female SE were significantly (P less than 0.001) heavier than middle-aged male and female LE respectively. The mean body weight for the male SE was 82 +/- 12 kg (mean +/- s.d.) against 69 +/- 9 kg for the LE, while it was 66 +/- 10 kg against 52 +/- 5 kg for the female SE and LE. The male and female SE also had a significantly higher percentage body fat in both age groups. In general, there was no difference in fat-free mass and activity level between the SE and LE. It is concluded that there exist groups of individuals who have a considerable difference in their EI and adiposity even though they have similar levels of activity and fat-free mass.