AbstractThein vitrobinding of estrone, estradiol‐17β, estriol, testosterone, dihydrotestosterone, and estrone‐3‐glucuronide by wheat, oat, and corn brans, oat hulls, cellulose, lignin, and chole‐styramine resin wasmeasured. The extent of steroid sequestration was characteristic and reproducible for each hormone. Cholestyramine bound an average of 90% of all the steroids tested, whereas cellulose bound the least (12%). Of the other substances tested, each bound the following percentage of unconjugated hormones: lignin, 87% wheat and oat brans, 45 % each; corn bran 44% and oat hulls, 32%. The conjugated steroid was less likely to bind than the unconjugated steroids. Lignin appeared to be an important component in the interaction with steroid hormones. The results support the hydrophobic nature of adsorption and suggest that the components of fiber in diet should be considered separately when evaluatingin vivometabolic effects.