The composition of the oxide film formed on iron in 0.1, 1 and 5 M NaOH was investigated using in-situ infrared spectroscopy (SNIFTIRS). For all three solutions Fe(OH)2 was found. In 1 M NaOH, alpha-FeOOH was also observed. An unassigned Fe(III) oxycompound was seen in 1 M and 5 M solutions, whose structure is proposed to be close to that of delta-FeOOH. A different Fe(III) oxycompound was detected in 0.1 M NaOH. The evolution of the layer with changing electrode potential and with repeated cycling is discussed.