This study provides preliminary data on the influence of ingestion of 15 g of dietary fiber daily for 4 weeks on weight change and serum iron concentrations in obese children. During two consecutive 4-week periods, subjects received either fiber/placebo supplements or placebo/fiber supplements. Initially, and after the fourth and eighth weeks, height, weight, and serum iron concentration were obtained. Diet records were maintained throughout the study. No significant differences (p less than or equal to 0.05) were found in weight change, energy, iron, and crude fiber intakes and serum iron concentrations of the subjects between periods of fiber and placebo supplementation. However, mean weight loss of subjects (336 g) was greater during fiber ingestion than during placebo ingestion (33 g). Due to the small sample size and the subjects' poor compliance, further studies are needed, with a larger sample size, to determine the effectiveness of different fibers in the treatment of obesity.