Amylose fractions, obtained from the starches of young grains of wheat by the usual method of complexing with n-butanol, bound small quantities of iodine compared with amylose isolated from mature tissues, suggesting a structural difference to the essentially unbranched α(1–4)glucan chain of the latter. However, fractionation by preparative ultra-centrifugation or by exclusion chromatography on agarose gel showed that these low binding values of amyloses isolated by complexing procedures from immature wheat were associated with incomplete separation from amylopectin and that the increase in the iodine binding of starch that accompanies its accumulation in developing wheat grains is due to an increase in the proportion of unbranched α(1–4)glucan.