Two patients presented with unilateral dilated and poorly reactive pupils and were found to have a previously unsuspected intraocular iron foreign body. Both of them had normal vision and one had normal color of the iris so that the condition was missed by several physicians. The pupils reacted normally to pilocarpine 1% and also showed response to dilute (0.1%) pilocarpine. There was no response to phospholine iodide. These findings indicate that the mydriasis was due to a local siderotic parasympathetic neuropathy of the pupil.