AbstractIn aqueous solutions of the amylase–iodine complex the concentration of free iodine [If]vafter reaching equilibrium (or closely approximating it) is determined by the following factors: temperature, pH, concentration of iodide ions and amylose, andDPof amylose. In the present paper the role of temperature, amylose concentration, andDPhas been investigated. At half‐saturation of amylose by iodine, the reciprocal value of free iodine defines the equilibrium constant: 1/[If]v=K. The relation between [If]v, in normality and temperature is the following: 5 + log [If]v= −(2.132/T) + 8.52, forDPn= 1290, 0.4 mg. amylose in 100 ml. 0.1NHCl. The value of the energy of activationEabetween 2 and 52°C. is 9.72 kcal./mole. The influence of amylose concentration [Am] on photometrically determined [If]v, at 20°C, in the range of 0.1–1.2 mg./100 ml. 0.1NHCl forDPn= 1290 is: 5 + log [If]v= 0.209 − 0.047 log [Am]. At [Am]= 0.6 mg. amylose/ 100 ml. 0.1NHCl and 20°C, the value of [If]vdepends onDPnas follows: 5 + log [If]v= 0.085 = + 0.222 log (104/DPn). These above equations are summarized by the relation: [If]v= exp {16.865 − (Ea/RT)}[Am]0.047(104/DPn)0.222×10−5Considering that the determination of [If]vby automatic photometric titration can be performed quickly and with appropriate reproducibility, this method is convenient for a rapid empirical and approximate determination ofDPof amylose on a microscale. The iodine‐binding capacity [IBC] as well as the value of λmax, have been also investigated as functions ofDPn, by photometric and by am