The object of this paper is to give details of a production method for123I, now in routine use at Harwell. We employ the (p, 5n) reaction, irradiating a liquid target of di-iodomethane (CH2I2) spiked with additional iodine, with 58 MeV protons. A yield of ∼9 mCi/μAh is obtained; the only detectable radionuclidic impurity is125I, present to the extent of ∼0.15% by activity at the time of separation of Xe from I.